diff --git a/composer.json b/composer.json
index 95b12fce..dc279835 100644
--- a/composer.json
+++ b/composer.json
@@ -31,5 +31,10 @@
         "allow-plugins": {
             "dealerdirect/phpcodesniffer-composer-installer": true
         }
+    },
+    "autoload": {
+        "psr-4": {
+            "DarkMatter\\": "includes/classes/"
+        }
     }
 }
diff --git a/dark-matter.php b/dark-matter.php
index b148add8..1180b54d 100644
--- a/dark-matter.php
+++ b/dark-matter.php
@@ -44,10 +44,22 @@
  */
 wp_cache_add_global_groups( 'dark-matter' );
 
-require_once DM_PATH . '/dark-matter/class-dm-pluginupdate.php';
+/**
+ * Include the PSR-4 autoloader.
+ */
+if ( file_exists( DM_PATH . 'vendor/autoload.php' ) ) {
+	require_once DM_PATH . 'vendor/autoload.php';
+}
+
+require_once DM_PATH . 'dark-matter/class-dm-pluginupdate.php';
 new DM_PluginUpdate();
 
 /**
- * Domain Mapping module.
+ * Non-autoloader files.
+ */
+require_once DM_PATH . '/includes/utility/functions.php';
+
+/**
+ * Let the magic - and bugs ... probably bugs! - begin.
  */
-require DM_PATH . '/domain-mapping/domain-mapping.php';
+\DarkMatter\DarkMatter::instance();
diff --git a/domain-mapping/classes/class-dm-ui.php b/domain-mapping/classes/class-dm-ui.php
deleted file mode 100644
index 105dd26b..00000000
--- a/domain-mapping/classes/class-dm-ui.php
+++ /dev/null
@@ -1,124 +0,0 @@
-<?php
-/**
- * Class DM_UI
- *
- * @package DM_UI
- * @since 2.0.0
- */
-
-defined( 'ABSPATH' ) || die;
-
-/**
- * Class DM_UI
- *
- * @since 2.0.0
- */
-class DM_UI {
-	/**
-	 * Constructor
-	 *
-	 * @since 2.0.0
-	 */
-	public function __construct() {
-		/**
-		 * The root website cannot be mapped.
-		 */
-		if ( is_main_site() ) {
-			return;
-		}
-
-		add_action( 'admin_menu', [ $this, 'admin_menu' ] );
-	}
-
-	/**
-	 * Initialise the admin menu and prep the hooks for the CSS and JavaScript
-	 * includes.
-	 *
-	 * @since 2.0.0
-	 *
-	 * @return void
-	 */
-	public function admin_menu() {
-		$hook_suffix = add_options_page(
-			__( 'Domain Mappings', 'dark-matter' ),
-			__( 'Domains', 'dark-matter' ),
-			$this->get_permission(),
-			'domains',
-			array(
-				$this,
-				'page',
-			)
-		);
-
-		add_action( 'load-' . $hook_suffix, array( $this, 'enqueue' ) );
-	}
-
-	/**
-	 * Enqueue assets for the Admin Page.
-	 *
-	 * @since 2.0.0
-	 *
-	 * @return void
-	 */
-	public function enqueue() {
-		$min = ( defined( 'SCRIPT_DEBUG' ) && SCRIPT_DEBUG ? '' : '.min' );
-
-		wp_register_script(
-			'dark-matter-domains',
-			DM_PLUGIN_URL . 'domain-mapping/build/domain-mapping' . $min . '.js',
-			[ 'wp-i18n' ],
-			DM_VERSION,
-			true
-		);
-
-		wp_localize_script(
-			'dark-matter-domains',
-			'dmSettings',
-			array(
-				'rest_root' => get_rest_url(),
-				'nonce'     => wp_create_nonce( 'wp_rest' ),
-			)
-		);
-
-		wp_enqueue_script( 'dark-matter-domains' );
-
-		wp_enqueue_style( 'dark-matter-domains', DM_PLUGIN_URL . 'domain-mapping/build/domain-mapping-style' . $min . '.css', [], DM_VERSION );
-	}
-
-	/**
-	 * Retrieve the capability that is required for using the admin page.
-	 *
-	 * @since 2.1.2
-	 *
-	 * @return string Capability that must be met to use the Admin page.
-	 */
-	public function get_permission() {
-		/**
-		 * Allows the override of the default permission for per site domain management.
-		 *
-		 * @since 2.1.2
-		 *
-		 * @param string $capability Capability required to manage domains (upgrade_network / Super Admin).
-		 * @param string $context The context the permission is checked.
-		 */
-		return apply_filters( 'dark_matter_domain_permission', 'upgrade_network', 'admin' );
-	}
-
-	/**
-	 * Very basic HTML output for the
-	 *
-	 * @since 2.0.0
-	 *
-	 * @return void
-	 */
-	public function page() {
-		if ( ! current_user_can( $this->get_permission() ) ) {
-			wp_die( esc_html__( 'You do not have permission to manage domains.', 'dark-matter' ) );
-		}
-		?>
-		<div id="root"></div>
-		<?php
-	}
-}
-
-new DM_UI();
diff --git a/domain-mapping/domain-mapping.php b/domain-mapping/domain-mapping.php
deleted file mode 100644
index edd7288d..00000000
--- a/domain-mapping/domain-mapping.php
+++ /dev/null
@@ -1,53 +0,0 @@
-<?php
-/**
- * Domain Mapping root file - used to include all the relevant files, etc., related to domain mapping functionality.
- *
- * @package DarkMatter
- *
- * @since 2.2.0
- */
-
-defined( 'ABSPATH' ) || die;
-
-/**
- * Domain type constants.
- */
-define( 'DM_DOMAIN_TYPE_MAIN', 1 );
-define( 'DM_DOMAIN_TYPE_MEDIA', 2 );
-
-require_once DM_PATH . '/domain-mapping/inc/compat.php';
-
-require_once DM_PATH . '/domain-mapping/classes/class-dm-media.php';
-require_once DM_PATH . '/domain-mapping/classes/class-dm-database.php';
-require_once DM_PATH . '/domain-mapping/classes/class-dm-domain.php';
-require_once DM_PATH . '/domain-mapping/classes/class-dm-healthchecks.php';
-require_once DM_PATH . '/domain-mapping/classes/class-dm-url.php';
-
-/**
- * Plugin compatibility.
- */
-require_once DM_PATH . '/domain-mapping/classes/third-party/class-dm-yoast.php';
-
-if ( ! defined( 'DARKMATTER_HIDE_UI' ) || ! DARKMATTER_HIDE_UI ) {
-	require_once DM_PATH . '/domain-mapping/classes/class-dm-ui.php';
-}
-
-require_once DM_PATH . '/domain-mapping/api/class-darkmatter-domains.php';
-require_once DM_PATH . '/domain-mapping/api/class-darkmatter-primary.php';
-require_once DM_PATH . '/domain-mapping/api/class-darkmatter-restrict.php';
-
-/**
- * Disable SSO if the COOKIE_DOMAIN constant is set.
- */
-if ( DM_HealthChecks::instance()->cookie_domain_dm_set() && ( ! defined( 'DARKMATTER_SSO_TYPE' ) || 'disable' !== DARKMATTER_SSO_TYPE ) ) {
-	require_once DM_PATH . '/domain-mapping/sso/class-dm-sso-cookie.php';
-}
-
-require_once DM_PATH . '/domain-mapping/rest/class-dm-rest-domains-controller.php';
-require_once DM_PATH . '/domain-mapping/rest/class-dm-rest-restricted-controller.php';
-
-if ( defined( 'WP_CLI' ) && WP_CLI ) {
-	require_once DM_PATH . '/domain-mapping/cli/class-darkmatter-domain-cli.php';
-	require_once DM_PATH . '/domain-mapping/cli/class-darkmatter-dropin-cli.php';
-	require_once DM_PATH . '/domain-mapping/cli/class-darkmatter-restrict-cli.php';
-}
diff --git a/domain-mapping/inc/compat.php b/domain-mapping/inc/compat.php
deleted file mode 100644
index b1d9174d..00000000
--- a/domain-mapping/inc/compat.php
+++ /dev/null
@@ -1,33 +0,0 @@
-<?php
-/**
- * Helper file to provide basic compatibilty for some popular plugins.
- *
- * @package DarkMatter
- * @since 2.0.0
- */
-
-defined( 'ABSPATH' ) || die();
-
-/**
- * Add support for logins on mapped domains for WooCommerce and bbPress.
- *
- * @since 2.0.0
- *
- * @return void
- */
-function dark_matter_compat_allow_logins() {
-	if (
-		/**
-		 * Detect if WooCommerce is installed.
-		 */
-		class_exists( 'WooCommerce' )
-	||
-		/**
-		 * Detect if bbPress is installed.
-		 */
-		class_exists( 'bbPress' )
-	) {
-		add_filter( 'darkmatter_allow_logins', '__return_true' );
-	}
-}
-add_action( 'init', 'dark_matter_compat_allow_logins' );
diff --git a/domain-mapping/inc/redirect.php b/domain-mapping/inc/redirect.php
deleted file mode 100644
index e69e1bcd..00000000
--- a/domain-mapping/inc/redirect.php
+++ /dev/null
@@ -1,186 +0,0 @@
-<?php
-/**
- * Redirect
- *
- * @package DarkMatter
- * @since 2.0.0
- */
-
-defined( 'ABSPATH' ) || die();
-
-/**
- * The function `rest_get_url_prefix()` is not available at this point in the
- * load process. Therefore we must substitute it with a close approximate of
- * what the function does.
- *
- * There is a side-effect of this. Basically if a site is to be setup with a
- * different prefix, in order for this to work, the `add_filter()` call would
- * need to be done in an Must-Use Plugin.
- */
-$rest_url_prefix = '/' . trim( apply_filters( 'rest_url_prefix', 'wp-json' ), '/' ) . '/';
-
-/**
- * Stop the execution of PHP code if any of the following conditions are true.
- * The constants noted below are all available and prior to the loading of the
- * sunrise.php file.
- */
-if (
-		/**
-		 * Do not attempt to redirect during the CLI command.
-		 */
-		( defined( 'WP_CLI' ) && WP_CLI )
-	||
-		/**
-		 * AJAX requests can be used on both the mapped and unmapped domains.
-		 */
-		( defined( 'DOING_AJAX' ) && DOING_AJAX )
-	||
-		/**
-		 * Do not attempt to redirect during the execution of cron.
-		 */
-		( defined( 'DOING_CRON' ) && DOING_CRON )
-	||
-		/**
-		 * XMLRPC Requests can be used on both the mapped and unmapped domains.
-		 */
-		( defined( 'XMLRPC_REQUEST' ) && XMLRPC_REQUEST )
-	||
-		/**
-		 * REST API can be used on both the mapped and unmapped domains.
-		 */
-		( ! empty( $_SERVER['REQUEST_URI'] ) && false !== strpos( $_SERVER['REQUEST_URI'], $rest_url_prefix ) ) // phpcs:ignore WordPress.Security.ValidatedSanitizedInput.InputNotSanitized
-	||
-		/**
-		 * Customizer is presented in an <iframe> over the unmapped domain.
-		 */
-		! empty( $_GET['customize_changeset_uuid'] ) // phpcs:ignore WordPress.Security.NonceVerification.Recommended
-	||
-		/**
-		 * Do not redirect Previews
-		 */
-		( ! empty( $_GET['preview'] ) || ! empty( $_GET['page_id'] ) || ! empty( $_GET['p'] ) ) // phpcs:ignore WordPress.Security.NonceVerification.Recommended
-	) {
-	return;
-}
-
-/**
- * Helper function which is used to determine if we need to perform a redirect
- * to the primary domain whilst retaining the remaining URI structure.
- *
- * @since 2.0.0
- *
- * @return void
- */
-function darkmatter_maybe_redirect() {
-	/**
-	 * Do not perform redirects if it is the main site.
-	 */
-	if ( is_main_site() ) {
-		return;
-	}
-
-	$request_uri = ( empty( $_SERVER['REQUEST_URI'] ) ? '' : wp_strip_all_tags( wp_unslash( $_SERVER['REQUEST_URI'] ) ) );
-
-	$request = ltrim( $request_uri, '/' );
-
-	/**
-	 * Determine if the request is one we shouldn't handle for redirects.
-	 */
-	$filename = basename( $request );
-	$filename = strtok( $filename, '?' );
-
-	$ajax_filenames = array(
-		'admin-post.php' => true,
-		'admin-ajax.php' => true,
-	);
-
-	/**
-	 * Check to see if the current request is an Admin Post action or an AJAX action. These two requests in Dark Matter
-	 * can be on either the admin domain or the primary domain.
-	 */
-	if ( ! empty( $filename ) && array_key_exists( $filename, $ajax_filenames ) ) {
-		return;
-	}
-
-	$original_blog = get_site();
-
-	$http_host = ( empty( $_SERVER['HTTP_HOST'] ) ? '' : wp_strip_all_tags( wp_unslash( $_SERVER['HTTP_HOST'] ) ) );
-
-	$host    = trim( $http_host, '/' );
-	$primary = DarkMatter_Primary::instance()->get();
-
-	$is_admin = false;
-
-	$admin_filenames = array(
-		'wp-login.php'    => true,
-		'wp-register.php' => true,
-	);
-
-	if ( is_admin() || ( ! empty( $filename ) && array_key_exists( $filename, $admin_filenames ) ) ) {
-		$is_admin = true;
-	}
-
-	/**
-	 * Dark Matter will disengage if the website is no longer public or is archived or deleted.
-	 */
-	if ( (int) $original_blog->public < 0 || '0' !== $original_blog->archived || '0' !== $original_blog->deleted ) {
-		return;
-	}
-
-	/**
-	 * If Allow Logins is enabled, then the `wp-login.php` request is to be made
-	 * available on both the primary mapped domain and admin domain.
-	 */
-	if ( ! apply_filters( 'darkmatter_allow_logins', false ) && $is_admin && $host === $original_blog->domain ) {
-		return;
-	}
-
-	/**
-	 * If there is no primary domain, there is nothing to do. Also make sure the
-	 * domain is active.
-	 */
-	if ( ! $primary || ! $original_blog || ! $primary->active || absint( $original_blog->public ) < 1 ) {
-		return;
-	}
-
-	if ( $is_admin && $host !== $original_blog->domain ) {
-		$is_ssl_admin = ( defined( 'FORCE_SSL_ADMIN' ) && FORCE_SSL_ADMIN );
-
-		$url = 'http' . ( $is_ssl_admin ? 's' : '' ) . '://' . $original_blog->domain . $original_blog->path . $request;
-	} elseif ( $host !== $primary->domain || is_ssl() !== $primary->is_https ) {
-		$url = 'http' . ( $primary->is_https ? 's' : '' ) . '://' . $primary->domain . '/' . $request;
-
-		/**
-		 * Make sure the Path - if this is a sub-folder Network - is removed from
-		 * the URL. For sub-domain Networks, the path will be a single forward slash
-		 * (/).
-		 */
-		if ( '/' !== $original_blog->path ) {
-			$path = '/' . trim( $original_blog->path, '/' ) . '/';
-			$url  = str_ireplace( $path, '/', $url );
-		}
-	}
-
-	/**
-	 * If the URL is empty, then there is no redirect to perform.
-	 */
-	if ( empty( $url ) ) {
-		return;
-	}
-
-	header( 'X-Redirect-By: Dark-Matter' );
-	header( 'Location:' . $url, true, 301 );
-
-	die;
-}
-
-/**
- * We use `muplugins_loaded` action (introduced in WordPress 2.8.0) rather than
- * the "ms_loaded" (introduced in WordPress 4.6.0).
- *
- * A hook on `muplugins_loaded` is used to ensure that WordPress has loaded the
- * Blog / Site globals. This is specifically useful when some one goes to the
- * Admin domain URL - http://my.sites.com/two/ - which is to redirect to the
- * primary domain - http://example.com.
- */
-add_action( 'muplugins_loaded', 'darkmatter_maybe_redirect', 20 );
diff --git a/domain-mapping/inc/sunrise.php b/domain-mapping/inc/sunrise.php
deleted file mode 100644
index c54f1beb..00000000
--- a/domain-mapping/inc/sunrise.php
+++ /dev/null
@@ -1,107 +0,0 @@
-<?php
-/**
- * Take the current request and perform the domain mapping for key global variables in WordPress.
- *
- * @package DarkMatter
- * @since 2.0.0
- */
-
-defined( 'ABSPATH' ) || die();
-
-wp_cache_add_global_groups( 'dark-matter' );
-
-if ( false === defined( 'SUNRISE_LOADED' ) ) {
-	define( 'SUNRISE_LOADED', true );
-}
-
-define( 'DARKMATTER_COOKIE_SET', ! defined( 'COOKIE_DOMAIN' ) );
-
-/**
- * Cannot utilise plugin_dir_path() as the inner function used is not available
- * and this is preferable to include more files than is realistically needed.
- */
-$dirname = str_replace( '/inc', '', dirname( __FILE__ ) );
-
-/**
- * Load the necessary parts of Dark Matter in to place.
- */
-require_once $dirname . '/classes/class-dm-domain.php';
-require_once $dirname . '/api/class-darkmatter-domains.php';
-require_once $dirname . '/api/class-darkmatter-primary.php';
-
-/**
- * Attempt to find the Site.
- */
-$fqdn = ( empty( $_SERVER['HTTP_HOST'] ) ? '' : $_SERVER['HTTP_HOST'] ); // phpcs:ignore WordPress.Security.ValidatedSanitizedInput.InputNotSanitized
-
-global $dm_domain;
-$dm_domain = DarkMatter_Domains::instance()->get( $fqdn );
-
-if ( $dm_domain && $dm_domain->active ) {
-	/**
-	 * Prepare all the global variables. This is require irrespective of whether
-	 * it is a primary or secondary domain.
-	 */
-	global $current_blog, $original_blog;
-	$current_blog = get_site( $dm_domain->blog_id ); // phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited
-
-	global $current_site;
-	$current_site = WP_Network::get_instance( $current_blog->site_id ); // phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited
-
-    // @codingStandardsIgnoreStart
-    global $blog_id;
-    $blog_id = $current_blog->blog_id;
-    global $site_id;
-    $site_id = $current_blog->site_id;
-    // @codingStandardsIgnoreEnd
-
-	/**
-	 * Dark Matter will disengage if the website is no longer public or is
-	 * archived or deleted.
-	 */
-	if ( (int) $current_blog->public < 0 || '0' !== $current_blog->archived || '0' !== $current_blog->deleted ) {
-		return;
-	}
-
-	/**
-	 * If the primary domain, then update the WP_Site properties to match the
-	 * mapped domain and not the admin domain.
-	 */
-	if ( $dm_domain->is_primary ) {
-		$original_blog = clone $current_blog;
-
-		$current_blog->domain = $dm_domain->domain;
-		$current_blog->path   = '/';
-
-		/**
-		 * Load and prepare the WordPress Network.
-		 */
-		global $current_site; // phpcs:ignore WordPressVIPMinimum.Variables.VariableAnalysis.VariableRedeclaration
-		$current_site = WP_Network::get_instance( $current_blog->site_id ); // phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited
-
-		if ( ! defined( 'COOKIE_DOMAIN' ) ) {
-			define( 'COOKIE_DOMAIN', $dm_domain->domain );
-		}
-
-		define( 'DOMAIN_MAPPING', true );
-
-		if ( empty( $current_site->blog_id ) ) {
-			$current_site->blog_id = get_main_site_id( $current_site->id );
-		}
-
-		/**
-		 * Set the other necessary globals to ensure WordPress functions correctly.
-		 */
-        // @codingStandardsIgnoreStart
-        global $blog_id;
-		$blog_id = $current_blog->blog_id;
-        global $site_id;
-		$site_id = $current_blog->site_id;
-        // @codingStandardsIgnoreEnd
-	}
-}
-
-/**
- * Determine if we should perform a redirect.
- */
-require_once $dirname . '/inc/redirect.php';
diff --git a/domain-mapping/sso/class-dm-sso-cookie.php b/domain-mapping/sso/class-dm-sso-cookie.php
deleted file mode 100644
index a23e76f3..00000000
--- a/domain-mapping/sso/class-dm-sso-cookie.php
+++ /dev/null
@@ -1,377 +0,0 @@
-<?php
-/**
- * There are three parts to the Domain Mapping single-sign on;
- *
- * 1) the JavaScript include on the header for each blog accessed through domain
- *    mapping.
- * 2) Create an authentication token and then redirect back to the mapped
- *    domain.
- * 3) Validate the token and then login the user with that token.
- *
- * The authentication token has to be created on the WordPress Network domian
- * and **NOT** the mapped domain. This is because the process uses Third Party
- * cookies and therefore the user is logged in on the WordPress Network domain.
- * Therefore an authentication token can only be generated by the WordPress
- * Network domain.
- *
- * The token is then provided in a URL request to the mapped domain blog and
- * then the token is used to create an session cookie to login the user.
- *
- * @package DarkMatter
- * @since 2.0.0
- */
-
-defined( 'ABSPATH' ) || die();
-
-// phpcs:disable WordPressVIPMinimum.Variables.RestrictedVariables.cache_constraints___SERVER__HTTP_USER_AGENT__
-
-/**
- * Class DM_SSO_Cookie
- *
- * @since 2.0.0
- */
-class DM_SSO_Cookie {
-	/**
-	 * Constructor.
-	 *
-	 * @since 2.0.0
-	 */
-	public function __construct() {
-		add_action( 'admin_post_dark_matter_dmsso', array( $this, 'login_token' ) );
-		add_action( 'admin_post_nopriv_dark_matter_dmsso', array( $this, 'login_token' ) );
-
-		add_action( 'admin_post_dark_matter_dmcheck', array( $this, 'logout_token' ) );
-		add_action( 'admin_post_nopriv_dark_matter_dmcheck', array( $this, 'logout_token' ) );
-
-		if ( ! $this->is_admin_domain() ) {
-			add_action( 'wp_head', array( $this, 'head_script' ) );
-			add_action( 'plugins_loaded', array( $this, 'validate_token' ) );
-		}
-	}
-
-	/**
-	 * Creates a nonce that isn't linked to a user, like the APIs in WordPress Core, but functions in a similar fashion.
-	 *
-	 * @since 2.0.4
-	 *
-	 * @param  string $action Value which creates the unique nonce.
-	 * @return string         Nonce token for use.
-	 */
-	private function create_shared_nonce( $action = '' ) {
-		$i = wp_nonce_tick();
-		return substr( wp_hash( $i . '|' . $action, 'nonce' ), -12, 10 );
-	}
-
-	/**
-	 * Verify a shared nonce.
-	 *
-	 * @since 2.0.4
-	 *
-	 * @see create_shared_nonce()
-	 *
-	 * @param  string $nonce  Nonce that was used and requires verification.
-	 * @param  string $action Value which provides the nonce uniqueness.
-	 * @return bool|int         An integer if the nonce check passed, 1 for 0-12 hours ago and 2 for 12-24 hours ago. False otherwise.
-	 */
-	private function verify_shared_nonce( $nonce = '', $action = '' ) {
-		if ( empty( $nonce ) ) {
-			return false;
-		}
-
-		$i = wp_nonce_tick();
-
-		/**
-		 * Nonce generated 0-12 hours ago
-		 */
-		$expected = substr( wp_hash( $i . '|' . $action, 'nonce' ), -12, 10 );
-		if ( hash_equals( $expected, $nonce ) ) {
-			return 1;
-		}
-
-		/**
-		 * Nonce generated 12-24 hours ago
-		 */
-		$expected = substr( wp_hash( ( $i - 1 ) . '|' . $action, 'nonce' ), -12, 10 );
-		if ( hash_equals( $expected, $nonce ) ) {
-			return 2;
-		}
-
-		/**
-		 * Invalid.
-		 */
-		return false;
-	}
-
-	/**
-	 * Determines if the current request is on the Admin Domain.
-	 *
-	 * @since 2.0.0
-	 *
-	 * @return bool True if current request is on the admin domain. False otherwise.
-	 */
-	private function is_admin_domain() {
-		$network = get_network();
-
-		$http_host = ( empty( $_SERVER['HTTP_HOST'] ) ? '' : wp_strip_all_tags( wp_unslash( $_SERVER['HTTP_HOST'] ) ) );
-
-		if ( ! empty( $network ) && false === stripos( $network->domain, $http_host ) ) {
-			return false;
-		}
-
-		return true;
-	}
-
-	/**
-	 * Create the JavaScript output include for logging a user in to the admin
-	 * when on the Mapped domain. This is ultimately what makes the Admin Bar
-	 * appear.
-	 *
-	 * @since 2.0.0
-	 *
-	 * @return void
-	 */
-	public function login_token() {
-		header( 'Content-Type: text/javascript' );
-
-		$this->nocache_headers();
-
-		/**
-		 * Ensure that the JavaScript is never empty.
-		 */
-		echo '// dm_sso' . PHP_EOL;
-
-		if ( is_user_logged_in() ) {
-			$referer = ( empty( $_SERVER['HTTP_REFERER'] ) ? '' : wp_strip_all_tags( wp_unslash( $_SERVER['HTTP_REFERER'] ) ) );
-
-			$action = sprintf(
-				'darkmatter-sso|%1$s|%2$s',
-				$referer,
-				md5( empty( $_SERVER['HTTP_USER_AGENT'] ) ? '' : wp_strip_all_tags( wp_unslash( $_SERVER['HTTP_USER_AGENT'] ) ) )
-			);
-
-			/**
-			 * Construct an authentication token which is passed back along with an
-			 * action flag to tell the front end to
-			 */
-			$url = add_query_arg(
-				array(
-					'__dm_action' => 'authorise',
-					'auth'        => wp_generate_auth_cookie( get_current_user_id(), time() + ( 2 * MINUTE_IN_SECONDS ) ),
-					'nonce'       => $this->create_shared_nonce( $action ),
-				),
-				$referer
-			);
-
-			printf( 'window.location.replace( "%1$s" );', esc_url_raw( $url ) );
-		}
-
-		die();
-	}
-
-	/**
-	 * Create the JavaScript output for handling the logout functionality.
-	 * Without this, users can end up in a state where they are logged out of
-	 * the Admin domain but remain perpetually logged in to the Mapped domains.
-	 *
-	 * @since 2.0.0
-	 *
-	 * @return void
-	 */
-	public function logout_token() {
-		header( 'Content-Type: text/javascript' );
-
-		$this->nocache_headers();
-
-		/**
-		 * Ensure that the JavaScript is never empty.
-		 */
-		echo '// dm_sso' . PHP_EOL;
-
-		if ( false === is_user_logged_in() ) {
-			$referer = ( empty( $_SERVER['HTTP_REFERER'] ) ? '' : wp_strip_all_tags( wp_unslash( $_SERVER['HTTP_REFERER'] ) ) );
-
-			$url = add_query_arg(
-				array(
-					'__dm_action' => 'logout',
-				),
-				$referer
-			);
-			printf( 'window.location.replace( "%1$s" );', esc_url_raw( $url ) );
-		}
-
-		die();
-	}
-
-	/**
-	 * Adds the <script> tag which references the admin action(s) for handling
-	 * cross-domain login and logout.
-	 *
-	 * @since 2.0.0
-	 *
-	 * @return void
-	 */
-	public function head_script() {
-		if ( is_main_site() || $this->is_admin_domain() ) {
-			return;
-		}
-
-		/**
-		 * Determine if the mapped domain is HTTPS and if so, ensure that the
-		 * Admin domain is also HTTPS. If it isn't, then we cannot do the third
-		 * party cookie authentication due to the differing protocols.
-		 */
-		if ( ( ! defined( 'FORCE_SSL_ADMIN' ) || ! FORCE_SSL_ADMIN ) && is_ssl() ) {
-			return;
-		}
-
-		$script_url = add_query_arg(
-			[
-				'action' => 'dark_matter_' . ( false === is_user_logged_in() ? 'dmsso' : 'dmcheck' ),
-			],
-			network_site_url( '/wp-admin/admin-post.php' )
-		);
-
-		/**
-		 * Check to see if the user is logged in to the current website on the mapped
-		 * domain. We then check the setting "Allow Logins?" to see if it is enabled.
-		 * In this scenario, the administrator has decided to let users log in only to
-		 * the map domain in some scenarios; likely utilising a Membership-like or
-		 * WooCommerce style plugin.
-		 */
-		if ( is_user_logged_in() && apply_filters( 'darkmatter_allow_logins', false ) ) {
-			$user = wp_get_current_user();
-
-			/**
-			 * Finally we check the user role to see if the user can edit content and
-			 * apply the default functionality for Contributor's and above. The logic
-			 * is like this because any one with Administrative or Content curation
-			 * ability will have access to the /wp-admin/ area which is on the admin
-			 * domain. Therefore ... users will need to login through the admin first.
-			 */
-			if ( is_a( $user, 'WP_User' ) && false === current_user_can( 'edit_posts' ) ) {
-				return;
-			}
-		}
-		?>
-		<script type="text/javascript">
-			( function () {
-				var s = document.createElement("script");
-				s.type = "text/javascript";
-				s.src = "<?php echo( esc_url( $script_url ) ); ?>&" + ( new Date() ).getTime();
-				document.head.appendChild( s );
-			} )();
-		</script>
-		<?php
-	}
-
-	/**
-	 * Sets the relevant no cache headers using the definition from WordPress Core.
-	 *
-	 * @since 2.0.0
-	 *
-	 * @return void
-	 */
-	public function nocache_headers() {
-		if ( headers_sent() ) {
-			return;
-		}
-
-		/**
-		 * Set the headers to prevent caching of the JavaScript include.
-		 */
-		$nocache_headers = wp_get_nocache_headers();
-
-		foreach ( $nocache_headers as $header_name => $header_value ) {
-			header( "{$header_name}: {$header_value}" );
-		}
-	}
-
-	/**
-	 * Handle the validation of the login token and logging in of a user. Also
-	 * handle the logout if that action is provided.
-	 *
-	 * @since 2.0.0
-	 *
-	 * @return void
-	 */
-	public function validate_token() {
-		$dm_action = ( empty( $_GET['__dm_action'] ) ? '' : wp_strip_all_tags( wp_unslash( $_GET['__dm_action'] ) ) );
-
-		/**
-		 * Ensure that URLs with the __dm_action query string are not cached by browsers.
-		 */
-		if ( ! empty( $dm_action ) ) {
-			$this->nocache_headers();
-		}
-
-		/**
-		 * If the validation token is provided on the admin domain, rather than the primary / mapped domain, then just
-		 * ignore it and end processing.
-		 */
-		if ( $this->is_admin_domain() ) {
-			return;
-		}
-
-		/**
-		 * First check to see if the authorise action is provided in the URL.
-		 */
-		if ( 'authorise' === $dm_action ) {
-			/**
-			 * Validate the token provided in the URL.
-			 */
-			$user_id = wp_validate_auth_cookie( wp_strip_all_tags( wp_unslash( $_GET['auth'] ) ), 'auth' );
-			$nonce   = wp_strip_all_tags( wp_unslash( $_GET['nonce'] ) );
-
-			$action = sprintf(
-				'darkmatter-sso|%1$s|%2$s',
-				( empty( $_SERVER['HTTP_REFERER'] ) ? '' : wp_strip_all_tags( wp_unslash( $_SERVER['HTTP_REFERER'] ) ) ),
-				md5( empty( $_SERVER['HTTP_USER_AGENT'] ) ? '' : wp_strip_all_tags( wp_unslash( $_SERVER['HTTP_USER_AGENT'] ) ) )
-			);
-
-			/**
-			 * Check if the validate token worked and we have a User ID. It will
-			 * display an error message or login the User if all works out well.
-			 */
-			if ( false === $user_id || ! $this->verify_shared_nonce( $nonce, $action ) ) {
-				wp_die( 'Oops! Something went wrong with logging in.' );
-			} else {
-				/**
-				 * Create the Login session cookie and redirect the user to the
-				 * current page with the URL querystrings for Domain Mapping SSO
-				 * removed.
-				 */
-				wp_set_auth_cookie( $user_id );
-
-                // phpcs:ignore WordPress.Security.SafeRedirect.wp_redirect_wp_redirect
-				wp_redirect( esc_url( remove_query_arg( array( '__dm_action', 'auth', 'nonce' ) ) ), 302, 'Dark-Matter' );
-				die();
-			}
-		} elseif ( 'logout' === $dm_action ) {
-			wp_logout();
-
-            // phpcs:ignore WordPress.Security.SafeRedirect.wp_redirect_wp_redirect
-			wp_redirect( esc_url( remove_query_arg( array( '__dm_action' ) ) ), 302, 'Dark-Matter' );
-
-			die();
-		}
-	}
-
-	/**
-	 * Return the Singleton Instance of the class.
-	 *
-	 * @since 2.0.0
-	 *
-	 * @return DM_SSO_Cookie
-	 */
-	public static function instance() {
-		static $instance = false;
-
-		if ( ! $instance ) {
-			$instance = new self();
-		}
-
-		return $instance;
-	}
-}
-
-DM_SSO_Cookie::instance();
diff --git a/includes/classes/DarkMatter.php b/includes/classes/DarkMatter.php
new file mode 100644
index 00000000..813c7036
--- /dev/null
+++ b/includes/classes/DarkMatter.php
@@ -0,0 +1,190 @@
+<?php
+/**
+ * Hello, this is the beginning of the Dark Matter plugin!
+ *
+ * @since 3.0.0
+ *
+ * @package DarkMatter
+ */
+
+namespace DarkMatter;
+
+use DarkMatter\DomainMapping;
+use DarkMatter\Interfaces\Registerable;
+use DarkMatter\SSO\Admin;
+use DarkMatter\SSO\Authenticate;
+use DarkMatter\SSO\Authorise;
+use DarkMatter\SSO\Testing;
+
+/**
+ * Class DarkMatter.
+ *
+ * @since 3.0.0
+ */
+class DarkMatter {
+	/**
+	 * Constructor
+	 *
+	 * @since 3.0.0
+	 */
+	public function __construct() {
+		add_action( 'rest_api_init', [ $this, 'register_rest' ] );
+
+		/**
+		 * Register and handle Domain Mapping module.
+		 */
+		$this->register_domainmapping();
+
+		/**
+		 * SSO is a web-based process and not needed in the CLI.
+		 */
+		if ( ! defined( 'WP_CLI' ) || ! WP_CLI ) {
+			$this->register_sso();
+		}
+	}
+
+	/**
+	 * Register a set of classes used by the Dark Matter plugin.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @param array $classes String of class names / namespaces to be instantiated.
+	 * @return array Array of the resultant objects.
+	 */
+	private function class_register( $classes = [] ) {
+		if ( empty( $classes ) ) {
+			return [];
+		}
+
+
+		$objs = [];
+		foreach ( $classes as $class ) {
+			$obj = new $class();
+
+			if ( $obj instanceof Registerable ) {
+				$obj->register();
+			}
+
+			if ( $obj instanceof \WP_CLI_Command ) {
+				$obj::define();
+			}
+
+			if ( $obj instanceof \WP_REST_Controller ) {
+				$obj->register_routes();
+			}
+		}
+
+		return $objs;
+	}
+
+	/**
+	 * Register the classes for Domain Mapping.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @return void
+	 */
+	public function register_domainmapping() {
+		/**
+		 * Domain type constants.
+		 */
+		define( 'DM_DOMAIN_TYPE_MAIN', 1 );
+		define( 'DM_DOMAIN_TYPE_MEDIA', 2 );
+
+		/**
+		 * Basic compatibility/configuration for bbPress and WooCommerce.
+		 */
+		if (
+			/**
+			 * Detect if WooCommerce is installed.
+			 */
+			class_exists( 'WooCommerce' )
+			||
+			/**
+			 * Detect if bbPress is installed.
+			 */
+			class_exists( 'bbPress' )
+		) {
+			add_filter( 'darkmatter_allow_logins', '__return_true' );
+		}
+
+		$domainmapping_classes = [
+			DomainMapping\Installer::class,
+			DomainMapping\Processor\Mapping::class,
+			DomainMapping\Processor\Media::class,
+		];
+
+		if (
+			( ! defined( 'DARKMATTER_HIDE_UI' ) || ! DARKMATTER_HIDE_UI )
+			&& ! is_main_site()
+		) {
+			$domainmapping_classes[] = DomainMapping\Admin\DomainSettings::class;
+		}
+
+		$domainmapping_classes[] = DomainMapping\Admin\HealthChecks::class;
+
+		if ( defined( 'WPSEO_VERSION' ) ) {
+			$domainmapping_classes = DomainMapping\Support\Yoast::class;
+		}
+
+		$this->class_register( $domainmapping_classes );
+
+		if ( defined( 'WP_CLI' ) && WP_CLI ) {
+			$this->class_register(
+				[
+					DomainMapping\CLI\Domains::class,
+					DomainMapping\CLI\Dropin::class,
+					DomainMapping\CLI\Restricted::class,
+				]
+			);
+		}
+	}
+
+	/**
+	 * Register REST routes. This is separate due to the need to be fired on the `rest_api_init` hook.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @return void
+	 */
+	public function register_rest() {
+		$this->class_register(
+			[
+				DomainMapping\REST\Domains::class,
+				DomainMapping\REST\Restricted::class,
+			]
+		);
+	}
+
+	/**
+	 * Single Sign-On functionality.
+	 *
+	 * @return void
+	 */
+	public function register_sso() {
+		$this->class_register(
+			[
+				Admin::class,
+				Authorise::class,
+				Authenticate::class,
+			]
+		);
+	}
+
+	/**
+	 * Return the Singleton Instance of the class.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @return DarkMatter
+	 */
+	public static function instance() {
+		static $instance = false;
+
+		if ( ! $instance ) {
+			$instance = new self();
+		}
+
+		return $instance;
+	}
+}
diff --git a/includes/classes/DomainMapping/Admin/DomainSettings.php b/includes/classes/DomainMapping/Admin/DomainSettings.php
new file mode 100644
index 00000000..f6f91b14
--- /dev/null
+++ b/includes/classes/DomainMapping/Admin/DomainSettings.php
@@ -0,0 +1,87 @@
+<?php
+/**
+ * Settings page for controlling domains.
+ *
+ * @since 3.0.0
+ *
+ * @package DarkMatterPlugin\DomainMapping
+ */
+
+namespace DarkMatter\DomainMapping\Admin;
+
+use DarkMatter\UI\AbstractAdminPage;
+
+/**
+ * Class DomainSettings
+ *
+ * Based on the old class called `DM_UI`.
+ *
+ * @since 3.0.0
+ */
+class DomainSettings extends AbstractAdminPage {
+	/**
+	 * Constructor
+	 *
+	 * @since 3.0.0
+	 */
+	public function __construct() {
+		$this->slug       = 'domains';
+		$this->menu_title = __( 'Domains', 'dark-matter' );
+		$this->page_title = __( 'Domain Mappings', 'dark-matter' );
+
+		/**
+		 * Allows the override of the default permission for per site domain management.
+		 *
+		 * @since 2.1.2
+		 *
+		 * @param string $capability Capability required to manage domains (upgrade_network / Super Admin).
+		 * @param string $context    The context the permission is checked.
+		 */
+		$this->permission = apply_filters( 'dark_matter_domain_permission', 'upgrade_network', 'admin' );
+	}
+
+	/**
+	 * Enqueue assets for the Admin Page.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @return void
+	 */
+	public function enqueue() {
+		$min = ( defined( 'SCRIPT_DEBUG' ) && SCRIPT_DEBUG ? '' : '.min' );
+
+		wp_register_script(
+			'dark-matter-domains',
+			DM_PLUGIN_URL . 'domain-mapping/build/domain-mapping' . $min . '.js',
+			[ 'wp-i18n' ],
+			DM_VERSION,
+			true
+		);
+
+		wp_localize_script(
+			'dark-matter-domains',
+			'dmSettings',
+			[
+				'rest_root' => get_rest_url(),
+				'nonce'     => wp_create_nonce( 'wp_rest' ),
+			]
+		);
+
+		wp_enqueue_script( 'dark-matter-domains' );
+
+		wp_enqueue_style( 'dark-matter-domains', DM_PLUGIN_URL . 'domain-mapping/build/domain-mapping-style' . $min . '.css', [], DM_VERSION );
+	}
+
+	/**
+	 * Output the HTML container for the React app.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @return void
+	 */
+	public function render() {
+		?>
+		<div id="root"></div>
+		<?php
+	}
+}
diff --git a/domain-mapping/classes/class-dm-healthchecks.php b/includes/classes/DomainMapping/Admin/HealthChecks.php
similarity index 92%
rename from domain-mapping/classes/class-dm-healthchecks.php
rename to includes/classes/DomainMapping/Admin/HealthChecks.php
index 8934af73..ced6f934 100644
--- a/domain-mapping/classes/class-dm-healthchecks.php
+++ b/includes/classes/DomainMapping/Admin/HealthChecks.php
@@ -1,19 +1,24 @@
 <?php
 /**
- * Class DM_HealthChecks
+ * Integration with WordPress Core's health setup.
  *
- * @package DarkMatter
  * @since 2.1.0
+ *
+ * @package DarkMatterPlugin\DomainMapping
  */
 
-defined( 'ABSPATH' ) || die;
+namespace DarkMatter\DomainMapping\Admin;
+
+use DarkMatter\DomainMapping\Manager\Primary;
 
 /**
- * Class DM_HealthChecks
+ * Class HealthChecks
+ *
+ * Previously called `DM_HealthChecks`.
  *
  * @since 2.1.0
  */
-class DM_HealthChecks {
+class HealthChecks {
 	/**
 	 * Constructor.
 	 *
@@ -76,7 +81,7 @@ public function cookie_domain_dm_set() {
 	 * @return bool True if sunrise.php exists. False otherwise.
 	 */
 	public function dropin_exists() {
-		return file_exists( DM_PATH . '/domain-mapping/sunrise.php' );
+		return file_exists( DM_PATH . '/includes/dropins/sunrise.php' );
 	}
 
 	/**
@@ -99,7 +104,7 @@ public function force_ssl_set() {
 	 */
 	public function is_dropin_latest() {
 		$destination = WP_CONTENT_DIR . '/sunrise.php';
-		$source      = DM_PATH . '/domain-mapping/sunrise.php';
+		$source      = DM_PATH . '/includes/dropins/sunrise.php';
 
 		return filesize( $destination ) === filesize( $source ) && md5_file( $destination ) === md5_file( $source );
 	}
@@ -115,10 +120,10 @@ public function test_cookie_domain() {
 		$result = [
 			'label'       => __( 'Dark Matter single-sign on (bringing the admin bar to the public-facing side) is enabled.', 'dark-matter' ),
 			'status'      => 'good',
-			'badge'       => array(
+			'badge'       => [
 				'label' => __( 'Domain Mapping', 'dark-matter' ),
 				'color' => 'green',
-			),
+			],
 			'description' => sprintf(
 				'<p>%s</p>',
 				__( 'Dark Matter single-sign on is enabled and can load the admin bar when WordPress users are visiting the public-facing side of your site.', 'dark-matter' )
@@ -155,10 +160,10 @@ public function test_dropin() {
 		$result = [
 			'label'       => __( 'Sunrise dropin is enabled and up-to-date.', 'dark-matter' ),
 			'status'      => 'good',
-			'badge'       => array(
+			'badge'       => [
 				'label' => __( 'Domain Mapping', 'dark-matter' ),
 				'color' => 'green',
-			),
+			],
 			'description' => sprintf(
 				'<p>%s</p>',
 				__( 'Sunrise is the name of the dropin file which maps custom domains to your WordPress sites.', 'dark-matter' )
@@ -219,16 +224,15 @@ public function test_primary_domain_set() {
 		$result = [
 			'label'       => __( 'You have a primary domain.', 'dark-matter' ),
 			'status'      => 'good',
-			'badge'       => array(
+			'badge'       => [
 				'label' => __( 'Domain Mapping', 'dark-matter' ),
 				'color' => 'green',
-			),
-			'description' => '',
+			],
 			'actions'     => '',
 			'test'        => 'darkmatter_domain_mapping_primary_domain_set',
 		];
 
-		$primary = DarkMatter_Primary::instance()->get();
+		$primary = Primary::instance()->get();
 
 		if ( empty( $primary ) ) {
 			$result['label']          = __( 'You have not a set a primary domain.', 'dark-matter' );
@@ -273,10 +277,10 @@ public function test_ssl() {
 		$result = [
 			'label'       => __( 'Your SSL configuration is compatible with Dark Matter.', 'dark-matter' ),
 			'status'      => 'good',
-			'badge'       => array(
+			'badge'       => [
 				'label' => __( 'Domain Mapping', 'dark-matter' ),
 				'color' => 'green',
-			),
+			],
 			'description' => sprintf(
 				'<p>%s</p>',
 				__( 'Your admin area is secured by HTTPS and compatible with domain mapping.', 'dark-matter' )
@@ -308,22 +312,4 @@ public function test_ssl() {
 
 		return $result;
 	}
-
-	/**
-	 * Return the Singleton Instance of the class.
-	 *
-	 * @since 2.1.0
-	 *
-	 * @return DM_HealthChecks
-	 */
-	public static function instance() {
-		static $instance = false;
-
-		if ( ! $instance ) {
-			$instance = new self();
-		}
-
-		return $instance;
-	}
 }
-DM_HealthChecks::instance();
diff --git a/domain-mapping/cli/class-darkmatter-domain-cli.php b/includes/classes/DomainMapping/CLI/Domains.php
similarity index 92%
rename from domain-mapping/cli/class-darkmatter-domain-cli.php
rename to includes/classes/DomainMapping/CLI/Domains.php
index 0fffc3bc..7ee4926e 100644
--- a/domain-mapping/cli/class-darkmatter-domain-cli.php
+++ b/includes/classes/DomainMapping/CLI/Domains.php
@@ -1,21 +1,28 @@
 <?php
 /**
- * Class DarkMatter_Domain_CLI
+ * CLI for managing domains.
  *
- * @package DarkMatter
  * @since 2.0.0
+ *
+ * @package DarkMatterPlugin\DomainMapping
  */
 
-defined( 'ABSPATH' ) || die;
+namespace DarkMatter\DomainMapping\CLI;
+
+use DarkMatter\DomainMapping\Manager;
+use WP_CLI;
+use WP_CLI_Command;
 
-// phpcs:disable PHPCompatibility.Keywords.ForbiddenNames.listFound -- Changing CLI for list would introduced backward compatibility (2.x.x) problems for pre-existing users.
+// phpcs:disable PHPCompatibility.Keywords.ForbiddenNames.listFound -- Changing CLI for list would introduce backward compatibility (2.x.x) problems for pre-existing users.
 
 /**
- * Class DarkMatter_Domain_CLI
+ * Class Domains
+ *
+ * Previously called `DarkMatter_Domain_CLI`.
  *
  * @since 2.0.0
  */
-class DarkMatter_Domain_CLI {
+class Domains extends WP_CLI_Command {
 	/**
 	 * Add a domain to a site on the WordPress Network.
 	 *
@@ -81,7 +88,7 @@ public function add( $args, $assoc_args ) {
 		/**
 		 * Add the domain.
 		 */
-		$db     = DarkMatter_Domains::instance();
+		$db     = Manager\Domain::instance();
 		$result = $db->add( $fqdn, $opts['primary'], $opts['https'], $opts['force'], ! $opts['disable'], $type );
 
 		if ( is_wp_error( $result ) ) {
@@ -121,6 +128,15 @@ private function check_type_opt( $type = '' ) {
 		return DM_DOMAIN_TYPE_MAIN;
 	}
 
+	/**
+	 * Include this CLI amongst the others.
+	 *
+	 * @return void
+	 */
+	public static function define() {
+		WP_CLI::add_command( 'darkmatter domain', self::class );
+	}
+
 	/**
 	 * List a domain for the current Site. If the the URL is omitted and the
 	 * command is run on the root Site, it will list all domains available for
@@ -166,12 +182,12 @@ public function list( $args, $assoc_args ) {
 			]
 		);
 
-		if ( ! in_array( $opts['format'], array( 'table', 'json', 'csv', 'yaml', 'count' ) ) ) {
+		if ( ! in_array( $opts['format'], [ 'table', 'json', 'csv', 'yaml', 'count' ] ) ) {
 			$opts['format'] = 'table';
 		}
 
 		if ( $opts['primary'] ) {
-			$db      = DarkMatter_Primary::instance();
+			$db      = Manager\Primary::instance();
 			$domains = $db->get_all();
 		} else {
 			/**
@@ -184,7 +200,7 @@ public function list( $args, $assoc_args ) {
 				$site_id = null;
 			}
 
-			$db      = DarkMatter_Domains::instance();
+			$db      = Manager\Domain::instance();
 			$domains = $db->get_domains( $site_id );
 		}
 
@@ -196,13 +212,13 @@ function ( $domain ) {
 				$no_val  = __( 'No', 'dark-matter' );
 				$yes_val = __( 'Yes', 'dark-matter' );
 
-				$columns = array(
+				$columns = [
 					'F.Q.D.N.' => $domain->domain,
 					'Primary'  => ( $domain->is_primary ? $yes_val : $no_val ),
 					'Protocol' => ( $domain->is_https ? 'HTTPS' : 'HTTP' ),
 					'Active'   => ( $domain->active ? $yes_val : $no_val ),
 					'Type'     => ( DM_DOMAIN_TYPE_MEDIA === $domain->type ? 'Media' : 'Main' ),
-				);
+				];
 
 				/**
 				 * If the query is the root Site and we are displaying all domains,
@@ -288,7 +304,7 @@ public function remove( $args, $assoc_args ) {
 			]
 		);
 
-		$db = DarkMatter_Domains::instance();
+		$db = Manager\Domain::instance();
 
 		/**
 		 * Remove the domain.
@@ -371,7 +387,7 @@ public function set( $args, $assoc_args ) {
 
 		$fqdn = $args[0];
 
-		$db            = DarkMatter_Domains::instance();
+		$db            = Manager\Domain::instance();
 		$domain_before = $db->get( $fqdn );
 
 		$opts = wp_parse_args(
@@ -462,4 +478,3 @@ public function set( $args, $assoc_args ) {
 		WP_CLI::success( $fqdn . __( ': successfully updated.', 'dark-matter' ) );
 	}
 }
-WP_CLI::add_command( 'darkmatter domain', 'DarkMatter_Domain_CLI' );
diff --git a/domain-mapping/cli/class-darkmatter-dropin-cli.php b/includes/classes/DomainMapping/CLI/Dropin.php
similarity index 81%
rename from domain-mapping/cli/class-darkmatter-dropin-cli.php
rename to includes/classes/DomainMapping/CLI/Dropin.php
index 546bedd9..beb629fb 100644
--- a/domain-mapping/cli/class-darkmatter-dropin-cli.php
+++ b/includes/classes/DomainMapping/CLI/Dropin.php
@@ -1,23 +1,26 @@
 <?php
 /**
- * Class DarkMatter_Dropin_CLI
+ * CLI for managing the Domain Mapping dropin (sunrise.php).
  *
- * @package DarkMatter
  * @since 2.0.0
+ *
+ * @package DarkMatterPlugin\DomainMapping
  */
 
-defined( 'ABSPATH' ) || die;
+namespace DarkMatter\DomainMapping\CLI;
 
-if ( ! defined( 'WP_CLI' ) ) {
-	return;
-}
+use DarkMatter\DomainMapping\Admin\HealthChecks;
+use WP_CLI;
+use WP_CLI_Command;
 
 /**
- * Class DarkMatter_Dropin_CLI
+ * Class Dropin
+ *
+ * Previously called `DarkMatter_Dropin_CLI`.
  *
  * @since 2.0.0
  */
-class DarkMatter_Dropin_CLI {
+class Dropin extends WP_CLI_Command {
 	/**
 	 * Helper command to see if the Sunrise dropin plugin within Dark Matter is
 	 * the same version as in use on the current WordPress installation.
@@ -30,8 +33,7 @@ class DarkMatter_Dropin_CLI {
 	 * @since 2.0.0
 	 */
 	public function check() {
-		$health_check = DM_HealthChecks::instance();
-
+		$health_check = new HealthChecks();
 		if ( $health_check->is_dropin_latest() ) {
 			WP_CLI::success( __( 'Current Sunrise dropin matches the Sunrise within Dark Matter plugin.', 'dark-matter' ) );
 			return;
@@ -40,6 +42,15 @@ public function check() {
 		WP_CLI::error( __( 'Sunrise dropin does not match the Sunrise within Dark Matter plugin. Consider using the "update" command to correct this issue.', 'dark-matter' ) );
 	}
 
+	/**
+	 * Include this CLI amongst the others.
+	 *
+	 * @return void
+	 */
+	public static function define() {
+		WP_CLI::add_command( 'darkmatter dropin', self::class );
+	}
+
 	/**
 	 * Upgrade the Sunrise dropin plugin to the latest version within the Dark
 	 * Matter plugin.
@@ -66,7 +77,7 @@ public function check() {
 	 */
 	public function update( $args, $assoc_args ) {
 		$destination = WP_CONTENT_DIR . '/sunrise.php';
-		$source      = DM_PATH . '/domain-mapping/sunrise.php';
+		$source      = DM_PATH . '/includes/dropins/sunrise.php';
 
 		$opts = wp_parse_args(
 			$assoc_args,
@@ -100,4 +111,3 @@ public function update( $args, $assoc_args ) {
 		}
 	}
 }
-WP_CLI::add_command( 'darkmatter dropin', 'DarkMatter_Dropin_CLI' );
diff --git a/domain-mapping/cli/class-darkmatter-restrict-cli.php b/includes/classes/DomainMapping/CLI/Restricted.php
similarity index 81%
rename from domain-mapping/cli/class-darkmatter-restrict-cli.php
rename to includes/classes/DomainMapping/CLI/Restricted.php
index ed2171fc..6d893409 100644
--- a/domain-mapping/cli/class-darkmatter-restrict-cli.php
+++ b/includes/classes/DomainMapping/CLI/Restricted.php
@@ -1,21 +1,26 @@
 <?php
 /**
- * Class DarkMatter_Restrict_CLI
+ * CLI for managing restricted domains.
  *
- * @package DarkMatter
  * @since 2.0.0
+ *
+ * @package DarkMatterPlugin\DomainMapping
  */
 
-defined( 'ABSPATH' ) || die;
+namespace DarkMatter\DomainMapping\CLI;
 
-// phpcs:disable PHPCompatibility.Keywords.ForbiddenNames.listFound -- Changing CLI for list would introduced backward compatibility (2.x.x) problems for pre-existing users.
+use \DarkMatter\DomainMapping\Manager;
+use WP_CLI;
+use WP_CLI_Command;
 
 /**
- * Class DarkMatter_Restrict_CLI
+ * Class Restricted
+ *
+ * Previously called `DarkMatter_Restrict_CLI`.
  *
  * @since 2.0.0
  */
-class DarkMatter_Restrict_CLI {
+class Restricted extends WP_CLI_Command {
 	/**
 	 * Add a domain to the restrict for the WordPress Network.
 	 *
@@ -41,7 +46,7 @@ public function add( $args, $assoc_args ) {
 
 		$fqdn = $args[0];
 
-		$restricted = DarkMatter_Restrict::instance();
+		$restricted = Manager\Restricted::instance();
 		$result     = $restricted->add( $fqdn );
 
 		if ( is_wp_error( $result ) ) {
@@ -51,6 +56,15 @@ public function add( $args, $assoc_args ) {
 		WP_CLI::success( $fqdn . __( ': is now restricted.', 'dark-matter' ) );
 	}
 
+	/**
+	 * Include this CLI amongst the others.
+	 *
+	 * @return void
+	 */
+	public static function define() {
+		WP_CLI::add_command( 'darkmatter restrict', self::class );
+	}
+
 	/**
 	 * Retrieve a list of all Restricted domains for the Network.
 	 *
@@ -90,11 +104,11 @@ public function list( $args, $assoc_args ) {
 			]
 		);
 
-		if ( ! in_array( $opts['format'], array( 'ids', 'table', 'json', 'csv', 'yaml', 'count' ) ) ) {
+		if ( ! in_array( $opts['format'], [ 'ids', 'table', 'json', 'csv', 'yaml', 'count' ] ) ) {
 			$opts['format'] = 'table';
 		}
 
-		$db = DarkMatter_Restrict::instance();
+		$db = Manager\Restricted::instance();
 
 		$restricted = $db->get();
 
@@ -146,7 +160,7 @@ public function remove( $args, $assoc_args ) {
 
 		$fqdn = $args[0];
 
-		$restricted = DarkMatter_Restrict::instance();
+		$restricted = Manager\Restricted::instance();
 		$result     = $restricted->delete( $fqdn );
 
 		if ( is_wp_error( $result ) ) {
@@ -156,4 +170,3 @@ public function remove( $args, $assoc_args ) {
 		WP_CLI::success( $fqdn . __( ': is no longer restricted.', 'dark-matter' ) );
 	}
 }
-WP_CLI::add_command( 'darkmatter restrict', 'DarkMatter_Restrict_CLI' );
diff --git a/domain-mapping/classes/class-dm-domain.php b/includes/classes/DomainMapping/Data/Domain.php
similarity index 86%
rename from domain-mapping/classes/class-dm-domain.php
rename to includes/classes/DomainMapping/Data/Domain.php
index 4986174b..d7109ea9 100644
--- a/domain-mapping/classes/class-dm-domain.php
+++ b/includes/classes/DomainMapping/Data/Domain.php
@@ -1,19 +1,22 @@
 <?php
 /**
- * Class DM_Domain
+ * Data type for a singular domain.
  *
- * @package DarkMatter
  * @since 2.0.0
+ *
+ * @package DarkMatterPlugin\DomainMapping
  */
 
-defined( 'ABSPATH' ) || die;
+namespace DarkMatter\DomainMapping\Data;
 
 /**
- * Class DM_Domain
+ * Class Domain
+ *
+ * Previously named `DM_Domain`.
  *
  * @since 2.0.0
  */
-class DM_Domain {
+class Domain {
 	/**
 	 * Database ID.
 	 *
@@ -83,7 +86,7 @@ class DM_Domain {
 	 *
 	 * @since 2.0.0
 	 *
-	 * @param DM_Domain|object $domain A domain object.
+	 * @param Domain|object $domain A domain object.
 	 */
 	public function __construct( $domain ) {
 		foreach ( get_object_vars( $domain ) as $key => $value ) {
diff --git a/includes/classes/DomainMapping/Helper.php b/includes/classes/DomainMapping/Helper.php
new file mode 100644
index 00000000..4781260b
--- /dev/null
+++ b/includes/classes/DomainMapping/Helper.php
@@ -0,0 +1,193 @@
+<?php
+/**
+ * Helper methods.
+ *
+ * @since 3.0.0
+ *
+ * @package DarkMatterPlugin\DomainMapping
+ */
+
+namespace DarkMatter\DomainMapping;
+
+use DarkMatter\DomainMapping\Manager\Primary;
+
+/**
+ * Class Helpers
+ *
+ * @since 3.0.0
+ */
+class Helper {
+	/**
+	 * Retrieves the FQDN as request from the URL.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @return string
+	 */
+	public function get_request_fqdn() {
+		$host = ( empty( $_SERVER['HTTP_HOST'] ) ? '' : $_SERVER['HTTP_HOST'] ); // phpcs:ignore WordPress.Security.ValidatedSanitizedInput.InputNotSanitized
+		return trim( $host, '/' );
+	}
+
+	/**
+	 * Get the filename from the request.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @return string
+	 */
+	public function get_request_filename() {
+		$request_uri = ( empty( $_SERVER['REQUEST_URI'] ) ? '' : wp_strip_all_tags( wp_unslash( $_SERVER['REQUEST_URI'] ) ) );
+		$request     = ltrim( $request_uri, '/' );
+
+		/**
+		 * Get the filename and remove any query strings.
+		 */
+		$filename = basename( $request );
+		return strtok( $filename, '?' );
+	}
+
+	/**
+	 * Determines if the request is admin, but unlike the `is_admin()`, will also check for the login and register page.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @param string $filename Filename.
+	 * @return bool True if admin, false otherwise.
+	 */
+	public function is_admin( $filename = '' ) {
+		$filename = empty( $filename ) ? $this->get_request_filename() : $filename;
+
+		$admin_filenames = [
+			'wp-login.php'    => true,
+			'wp-register.php' => true,
+		];
+
+		if ( is_admin() || ( ! empty( $filename ) && array_key_exists( $filename, $admin_filenames ) ) ) {
+			return true;
+		}
+
+		return false;
+	}
+
+	/**
+	 * Checks the supply blog/site to ensure it is public.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @param \WP_Site $blog Blog to check.
+	 * @return bool True if public. False otherwise.
+	 */
+	public function is_public( $blog ) {
+		/**
+		 * Make sure we have the right kind of object.
+		 */
+		if ( ! $blog instanceof \WP_Site ) {
+			return false;
+		}
+
+		return (
+			/**
+			 * Check the current blog is public and be compatible with plugins such as Restricted Site Access.
+			 */
+			0 < (int) $blog->public
+			/**
+			 * Check the current blog has not been archived.
+			 */
+			&& 0 === (int) $blog->archived
+			/**
+			 * Check the current blog has not been "soft" deleted.
+			 */
+			&& 0 === (int) $blog->deleted
+		);
+	}
+
+	/**
+	 * Map the primary domain on the passed in value if it contains the unmapped URL and the Site has a primary domain.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @param  mixed   $value   Potentially a value containing the site's unmapped URL.
+	 * @param  integer $blog_id Site (Blog) ID for the URL which is being mapped.
+	 * @return string           If unmapped URL is found, then returns the primary URL. Untouched otherwise.
+	 */
+	public function map( $value = '', $blog_id = 0 ) {
+		/**
+		 * Ensure that we are working with a string.
+		 */
+		if ( ! is_string( $value ) ) {
+			return $value;
+		}
+
+		/**
+		 * Retrieve the current blog.
+		 */
+		$blog    = get_site( absint( $blog_id ) );
+		$primary = Primary::instance()->get( $blog->blog_id );
+
+		$unmapped = untrailingslashit( $blog->domain . $blog->path );
+
+		/**
+		 * If there is no primary domain or the unmapped version cannot be found
+		 * then we return the value as-is.
+		 */
+		if ( empty( $primary ) || false === stripos( $value, $unmapped ) ) {
+			return $value;
+		}
+
+		$domain = 'http' . ( $primary->is_https ? 's' : '' ) . '://' . $primary->domain;
+
+		return preg_replace( "#https?://{$unmapped}#", $domain, $value );
+	}
+
+	/**
+	 * Converts a URL from a mapped domain to the admin domain. This will only convert a URL which is the primary
+	 * domain.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @param  mixed $value Potentially a value containing the site's unmapped URL.
+	 * @return mixed        If unmapped URL is found, then returns the primary URL. Untouched otherwise.
+	 */
+	public function unmap( $value = '' ) {
+		/**
+		 * Ensure that we are working with a string.
+		 */
+		if ( ! is_string( $value ) ) {
+			return $value;
+		}
+
+		/**
+		 * Retrieve the current blog.
+		 */
+		$blog    = get_site();
+		$primary = Primary::instance()->get();
+
+		/**
+		 * If there is no primary domain or the primary domain cannot be found
+		 * then we return the value as-is.
+		 */
+		if ( empty( $primary ) || false === stripos( $value, $primary->domain ) ) {
+			return $value;
+		}
+
+		$unmapped = 'http' . ( $primary->is_https ? 's' : '' ) . '://' . untrailingslashit( $blog->domain . $blog->path );
+
+		return preg_replace( "#https?://{$primary->domain}#", $unmapped, $value );
+	}
+
+	/**
+	 * Return the Singleton Instance of the class.
+	 *
+	 * @return Helper
+	 */
+	public static function instance() {
+		static $instance = false;
+
+		if ( ! $instance ) {
+			$instance = new self();
+		}
+
+		return $instance;
+	}
+}
diff --git a/domain-mapping/classes/class-dm-database.php b/includes/classes/DomainMapping/Installer.php
similarity index 79%
rename from domain-mapping/classes/class-dm-database.php
rename to includes/classes/DomainMapping/Installer.php
index 752bbd60..944820e3 100644
--- a/domain-mapping/classes/class-dm-database.php
+++ b/includes/classes/DomainMapping/Installer.php
@@ -1,26 +1,29 @@
 <?php
 /**
- * Class DM_Database
+ * Handles any installation logic needed for the Domain Mapping module.
  *
- * @package DarkMatter
  * @since 2.0.0
+ *
+ * @package DarkMatterPlugin\DomainMapping
  */
 
-defined( 'ABSPATH' ) || die;
+namespace DarkMatter\DomainMapping;
 
 /**
- * Class DM_Database
+ * Class Installer
+ *
+ * Previously called `DM_Database`.
  *
  * @since 2.0.0
  */
-class DM_Database {
+class Installer {
 	/**
 	 * Constructor.
 	 *
 	 * @since 2.0.0
 	 */
 	public function __construct() {
-		add_action( 'init', array( $this, 'maybe_upgrade' ) );
+		add_action( 'init', [ $this, 'maybe_upgrade' ] );
 	}
 
 	/**
@@ -88,22 +91,4 @@ public function upgrade_restrict() {
 
 		dbDelta( $sql );
 	}
-
-	/**
-	 * Return the Singleton Instance of the class.
-	 *
-	 * @since 2.0.0
-	 *
-	 * @return DM_Database
-	 */
-	public static function instance() {
-		static $instance = false;
-
-		if ( ! $instance ) {
-			$instance = new self();
-		}
-
-		return $instance;
-	}
 }
-DM_Database::instance();
diff --git a/domain-mapping/api/class-darkmatter-domains.php b/includes/classes/DomainMapping/Manager/Domain.php
similarity index 84%
rename from domain-mapping/api/class-darkmatter-domains.php
rename to includes/classes/DomainMapping/Manager/Domain.php
index 2fee1b71..5b98e4ac 100644
--- a/domain-mapping/api/class-darkmatter-domains.php
+++ b/includes/classes/DomainMapping/Manager/Domain.php
@@ -1,19 +1,24 @@
 <?php
 /**
- * Class DarkMatter_Domains
+ * Handles the management of domains.
  *
- * @package DarkMatter
  * @since 2.0.0
+ *
+ * @package DarkMatterPlugin\DomainMapping
  */
 
-defined( 'ABSPATH' ) || die;
+namespace DarkMatter\DomainMapping\Manager;
+
+use DarkMatter\DomainMapping\Data;
 
 /**
- * Class DarkMatter_Domains
+ * Class Domain
+ *
+ * Previously called `DarkMatter_Domains`.
  *
  * @since 2.0.0
  */
-class DarkMatter_Domains {
+class Domain {
 	/**
 	 * The Domain Mapping table name for use by the various methods.
 	 *
@@ -59,8 +64,8 @@ public function __construct() {
 		 */
 		$this->wpdb = $wpdb;
 
-		if ( defined( 'DM_NETWORK_MEDIA' ) && ! empty( DM_NETWORK_MEDIA ) ) {
-			$this->network_media = DM_NETWORK_MEDIA;
+		if ( defined( '\DM_NETWORK_MEDIA' ) && ! empty( \DM_NETWORK_MEDIA ) ) {
+			$this->network_media = \DM_NETWORK_MEDIA;
 		}
 	}
 
@@ -70,11 +75,11 @@ public function __construct() {
 	 * @since 2.0.0
 	 *
 	 * @param  string $fqdn Fully qualified domain name.
-	 * @return WP_Error|boolean       True on pass. WP_Error on failure.
+	 * @return \WP_Error|boolean       True on pass. WP_Error on failure.
 	 */
 	private function _basic_check( $fqdn = '' ) {
 		if ( empty( $fqdn ) ) {
-			return new WP_Error( 'empty', __( 'Please include a fully qualified domain name to be added.', 'dark-matter' ) );
+			return new \WP_Error( 'empty', __( 'Please include a fully qualified domain name to be added.', 'dark-matter' ) );
 		}
 
 		/**
@@ -90,7 +95,7 @@ private function _basic_check( $fqdn = '' ) {
 		}
 
 		if ( ! empty( $domain_parts['path'] ) || ! empty( $domain_parts['port'] ) || ! empty( $domain_parts['query'] ) ) {
-			return new WP_Error( 'unsure', __( 'The domain provided contains path, port, or query string information. Please removed this before continuing.', 'dark-matter' ) );
+			return new \WP_Error( 'unsure', __( 'The domain provided contains path, port, or query string information. Please removed this before continuing.', 'dark-matter' ) );
 		}
 
 		$fqdn = $domain_parts['host'];
@@ -99,20 +104,20 @@ private function _basic_check( $fqdn = '' ) {
 		 * Check to ensure we have a valid domain to work with.
 		 */
 		if ( ! filter_var( $fqdn, FILTER_VALIDATE_DOMAIN, FILTER_FLAG_HOSTNAME ) ) {
-			return new WP_Error( 'domain', __( 'The domain is not valid.', 'dark-matter' ) );
+			return new \WP_Error( 'domain', __( 'The domain is not valid.', 'dark-matter' ) );
 		}
 
 		if ( defined( 'DOMAIN_CURRENT_SITE' ) && DOMAIN_CURRENT_SITE === $fqdn ) {
-			return new WP_Error( 'wp-config', __( 'You cannot configure the WordPress Network primary domain.', 'dark-matter' ) );
+			return new \WP_Error( 'wp-config', __( 'You cannot configure the WordPress Network primary domain.', 'dark-matter' ) );
 		}
 
 		if ( is_main_site() ) {
-			return new WP_Error( 'root', __( 'Domains cannot be mapped to the main / root Site.', 'dark-matter' ) );
+			return new \WP_Error( 'root', __( 'Domains cannot be mapped to the main / root Site.', 'dark-matter' ) );
 		}
 
-		$reserve = DarkMatter_Restrict::instance();
+		$reserve = \DarkMatter\DomainMapping\Manager\Restricted::instance();
 		if ( $reserve->is_exist( $fqdn ) ) {
-			return new WP_Error( 'reserved', __( 'This domain has been reserved.', 'dark-matter' ) );
+			return new \WP_Error( 'reserved', __( 'This domain has been reserved.', 'dark-matter' ) );
 		}
 
 		/**
@@ -153,7 +158,7 @@ private function _clear_caches( $fqdn = '' ) {
 	 * @param  boolean $force      Whether the update should be forced.
 	 * @param  boolean $active     Default is active. Set to false if you wish to add a domain but not make it active.
 	 * @param  integer $type       Domain type. Defaults to `1`, which is "main".
-	 * @return DM_Domain|WP_Error             DM_Domain on success. WP_Error on failure.
+	 * @return Data\Domain|\WP_Error Domain on success. WP_Error on failure.
 	 */
 	public function add( $fqdn = '', $is_primary = false, $is_https = false, $force = true, $active = true, $type = DM_DOMAIN_TYPE_MAIN ) {
 		$fqdn = $this->_basic_check( $fqdn );
@@ -166,10 +171,10 @@ public function add( $fqdn = '', $is_primary = false, $is_https = false, $force
 		 * Check that the FQDN is not already stored in the database.
 		 */
 		if ( $this->is_exist( $fqdn ) ) {
-			return new WP_Error( 'exists', __( 'This domain is already assigned to a Site.', 'dark-matter' ) );
+			return new \WP_Error( 'exists', __( 'This domain is already assigned to a Site.', 'dark-matter' ) );
 		}
 
-		$dm_primary = DarkMatter_Primary::instance();
+		$dm_primary = Primary::instance();
 
 		if ( $is_primary ) {
 			$primary_domain = $dm_primary->get();
@@ -179,7 +184,7 @@ public function add( $fqdn = '', $is_primary = false, $is_https = false, $force
 			 */
 			if ( ! empty( $primary_domain ) ) {
 				if ( ! $force ) {
-					return new WP_Error( 'primary', __( 'You cannot add this domain as the primary domain without using the force flag.', 'dark-matter' ) );
+					return new \WP_Error( 'primary', __( 'You cannot add this domain as the primary domain without using the force flag.', 'dark-matter' ) );
 				}
 			}
 		}
@@ -188,29 +193,29 @@ public function add( $fqdn = '', $is_primary = false, $is_https = false, $force
 		 * Check the type is valid.
 		 */
 		if ( DM_DOMAIN_TYPE_MAIN !== $type && DM_DOMAIN_TYPE_MEDIA !== $type ) {
-			return new WP_Error( 'type', __( 'The type for the new domain is not supported.', 'dark-matter' ) );
+			return new \WP_Error( 'type', __( 'The type for the new domain is not supported.', 'dark-matter' ) );
 		}
 
-		$_domain = array(
+		$_domain = [
 			'active'     => ( ! $active ? false : true ),
 			'blog_id'    => get_current_blog_id(),
 			'domain'     => $fqdn,
 			'is_primary' => ( ! $is_primary ? false : true ),
 			'is_https'   => ( ! $is_https ? false : true ),
 			'type'       => ( ! empty( $type ) ? $type : DM_DOMAIN_TYPE_MAIN ),
-		);
+		];
 
 		$result = $this->wpdb->insert(
 			$this->dm_table,
 			$_domain,
-			array(
+			[
 				'%d',
 				'%d',
 				'%s',
 				'%d',
 				'%d',
 				'%d',
-			)
+			]
 		);
 
 		if ( $result ) {
@@ -235,7 +240,7 @@ public function add( $fqdn = '', $is_primary = false, $is_https = false, $force
 				$this->primary_set( $fqdn, get_current_blog_id() );
 			}
 
-			$dm_domain = new DM_Domain( (object) $_domain );
+			$dm_domain = new Data\Domain( (object) $_domain );
 
 			$this->update_last_changed();
 
@@ -247,14 +252,14 @@ public function add( $fqdn = '', $is_primary = false, $is_https = false, $force
 			 *
 			 * @since 2.0.0
 			 *
-			 * @param DM_Domain $dm_domain Domain object of the newly added Domain.
+			 * @param Data\Domain $dm_domain Domain object of the newly added Domain.
 			 */
 			do_action( 'darkmatter_domain_add', $dm_domain );
 
 			return $dm_domain;
 		}
 
-		return new WP_Error( 'unknown', __( 'Sorry, the domain could not be added. An unknown error occurred.', 'dark-matter' ) );
+		return new \WP_Error( 'unknown', __( 'Sorry, the domain could not be added. An unknown error occurred.', 'dark-matter' ) );
 	}
 
 	/**
@@ -322,7 +327,7 @@ public function clear_cache_for_domain_type( $type = DM_DOMAIN_TYPE_MAIN, $site_
 	 *
 	 * @param  string  $fqdn FQDN to be deleted.
 	 * @param  boolean $force Force the FQDN to be deleted, even if it is the primary domain.
-	 * @return WP_Error|boolean True on success. False otherwise.
+	 * @return \WP_Error|boolean True on success. False otherwise.
 	 */
 	public function delete( $fqdn = '', $force = true ) {
 		$fqdn = $this->_basic_check( $fqdn );
@@ -335,7 +340,7 @@ public function delete( $fqdn = '', $force = true ) {
 		 * Cannot delete what does not exist.
 		 */
 		if ( ! $this->is_exist( $fqdn ) ) {
-			return new WP_Error( 'exists', __( 'The domain cannot be found.', 'dark-matter' ) );
+			return new \WP_Error( 'exists', __( 'The domain cannot be found.', 'dark-matter' ) );
 		}
 
 		/**
@@ -344,7 +349,7 @@ public function delete( $fqdn = '', $force = true ) {
 		$_domain = $this->get( $fqdn );
 
 		if ( ! $_domain || get_current_blog_id() !== $_domain->blog_id ) {
-			return new WP_Error( 'not found', __( 'The domain cannot be found.', 'dark-matter' ) );
+			return new \WP_Error( 'not found', __( 'The domain cannot be found.', 'dark-matter' ) );
 		}
 
 		/**
@@ -355,7 +360,7 @@ public function delete( $fqdn = '', $force = true ) {
 			if ( $force ) {
 				$this->primary_unset( $_domain->domain, $_domain->blog_id );
 			} else {
-				return new WP_Error( 'primary', __( 'This domain is the primary domain for this Site. Please provide the force flag to delete.', 'dark-matter' ) );
+				return new \WP_Error( 'primary', __( 'This domain is the primary domain for this Site. Please provide the force flag to delete.', 'dark-matter' ) );
 			}
 		}
 
@@ -381,14 +386,14 @@ public function delete( $fqdn = '', $force = true ) {
 			 *
 			 * @since 2.0.0
 			 *
-			 * @param DM_Domain $_domain Domain object that was deleted.
+			 * @param Data\Domain $_domain Domain object that was deleted.
 			 */
 			do_action( 'darkmatter_domain_delete', $_domain );
 
 			return true;
 		}
 
-		return new WP_Error( 'unknown', __( 'Sorry, the domain could not be deleted. An unknown error occurred.', 'dark-matter' ) );
+		return new \WP_Error( 'unknown', __( 'Sorry, the domain could not be deleted. An unknown error occurred.', 'dark-matter' ) );
 
 	}
 
@@ -398,7 +403,7 @@ public function delete( $fqdn = '', $force = true ) {
 	 * @since 2.0.0
 	 *
 	 * @param  string $fqdn FQDN to search for.
-	 * @return DM_Domain|boolean       Domain object. False on failure or not found.
+	 * @return Data\Domain|boolean Domain object. False on failure or not found.
 	 */
 	public function find( $fqdn = '' ) {
 		if ( empty( $fqdn ) ) {
@@ -414,7 +419,7 @@ public function find( $fqdn = '' ) {
 	 * @since 2.0.0
 	 *
 	 * @param  string $fqdn FQDN to search for.
-	 * @return DM_Domain|boolean       Domain object. False otherwise.
+	 * @return Data\Domain|boolean Domain object. False otherwise.
 	 */
 	public function get( $fqdn = '' ) {
 		if ( empty( $fqdn ) ) {
@@ -478,7 +483,7 @@ public function get( $fqdn = '' ) {
 		/**
 		 * Return the DM_Domain object version.
 		 */
-		return new DM_Domain( (object) $_domain );
+		return new Data\Domain( (object) $_domain );
 	}
 
 	/**
@@ -515,7 +520,7 @@ public function get_domains_by_type( $type = DM_DOMAIN_TYPE_MEDIA, $site_id = 0,
 				 * Convert the domains into DM_Domain objects.
 				 */
 				foreach ( $this->network_media as $i => $media_domain ) {
-					$media_domains[ $i ] = new DM_Domain(
+					$media_domains[ $i ] = new Data\Domain(
 						(object) [
 							'active'     => true,
 							'blog_id'    => get_current_blog_id(),
@@ -576,7 +581,7 @@ public function get_domains_by_type( $type = DM_DOMAIN_TYPE_MEDIA, $site_id = 0,
 		/**
 		 * Retrieve the domain details, probably from cache, and get an array of `DM_Domain` objects.
 		 */
-		$domains = array();
+		$domains = [];
 
 		foreach ( $_domains as $_domain ) {
 			$domains[] = $this->get( $_domain );
@@ -615,7 +620,7 @@ public function get_domains( $site_id = 0 ) {
 		/**
 		 * Retrieve the domain details from the cache. If the cache is
 		 */
-		$domains = array();
+		$domains = [];
 
 		foreach ( $_domains as $_domain ) {
 			$domains[] = $this->get( $_domain );
@@ -671,7 +676,7 @@ public function is_reserved( $fqdn = '' ) {
 	 * @return void
 	 */
 	private function primary_set( $domain = '', $blog_id = 0 ) {
-		$current_primary = DarkMatter_Primary::instance()->get( $blog_id );
+		$current_primary = \DarkMatter\DomainMapping\Manager\Primary::instance()->get( $blog_id );
 
 		if ( ! empty( $current_primary ) && $domain !== $current_primary->domain ) {
 			$this->update( $current_primary->domain, false, null, true, $current_primary->active );
@@ -748,7 +753,7 @@ public function reserve( $fqdn = '' ) {
 	 * @param  boolean $force      Whether the update should be forced.
 	 * @param  boolean $active     Default is active. Set to false if you wish to add a domain but not make it active.
 	 * @param  integer $type       Domain type. Defaults to `null`, do not change current value. Accepts `1` for main and `2` for Media.
-	 * @return DM_Domain|WP_Error             DM_Domain on success. WP_Error on failure.
+	 * @return Data\Domain|\WP_Error DM_Domain on success. WP_Error on failure.
 	 */
 	public function update( $fqdn = '', $is_primary = null, $is_https = null, $force = true, $active = true, $type = null ) {
 		$fqdn = $this->_basic_check( $fqdn );
@@ -760,16 +765,16 @@ public function update( $fqdn = '', $is_primary = null, $is_https = null, $force
 		$domain_before = $this->get( $fqdn );
 
 		if ( ! $domain_before ) {
-			return new WP_Error( 'not found', __( 'Cannot find the domain to update.', 'dark-matter' ) );
+			return new \WP_Error( 'not found', __( 'Cannot find the domain to update.', 'dark-matter' ) );
 		}
 
-		$dm_primary = DarkMatter_Primary::instance();
+		$dm_primary = \DarkMatter\DomainMapping\Manager\Primary::instance();
 
-		$_domain = array(
+		$_domain = [
 			'active'  => ( ! $active ? false : true ),
 			'blog_id' => $domain_before->blog_id,
 			'domain'  => $fqdn,
-		);
+		];
 
 		/**
 		 * Determine if there is an attempt to update the "is primary" field.
@@ -779,7 +784,7 @@ public function update( $fqdn = '', $is_primary = null, $is_https = null, $force
 			 * Any update to the "is primary" requires the force flag.
 			 */
 			if ( ! $force ) {
-				return new WP_Error( 'primary', __( 'You cannot update the primary flag without setting the force parameter to true', 'dark-matter' ) );
+				return new \WP_Error( 'primary', __( 'You cannot update the primary flag without setting the force parameter to true', 'dark-matter' ) );
 			}
 
 			$_domain['is_primary'] = $is_primary;
@@ -796,16 +801,16 @@ public function update( $fqdn = '', $is_primary = null, $is_https = null, $force
 			if ( DM_DOMAIN_TYPE_MAIN === $type || DM_DOMAIN_TYPE_MEDIA === $type ) {
 				$_domain['type'] = $type;
 			} else {
-				return new WP_Error( 'type', __( 'The type for the new domain is not supported.', 'dark-matter' ) );
+				return new \WP_Error( 'type', __( 'The type for the new domain is not supported.', 'dark-matter' ) );
 			}
 		}
 
 		$result = $this->wpdb->update(
 			$this->dm_table,
 			$_domain,
-			array(
+			[
 				'id' => $domain_before->id,
-			)
+			]
 		);
 
 		if ( $result ) {
@@ -841,7 +846,7 @@ public function update( $fqdn = '', $is_primary = null, $is_https = null, $force
 				$this->primary_unset( $domain_before->domain, $domain_before->blog_id );
 			}
 
-			$domain_after = new DM_Domain( (object) $_domain );
+			$domain_after = new Data\Domain( (object) $_domain );
 
 			$this->update_last_changed();
 
@@ -850,15 +855,15 @@ public function update( $fqdn = '', $is_primary = null, $is_https = null, $force
 			 *
 			 * @since 2.0.0
 			 *
-			 * @param DM_Domain $domain_after  Domain object after the changes have been applied successfully.
-			 * @param DM_Domain $domain_before Domain object before.
+			 * @param Data\Domain $domain_after  Domain object after the changes have been applied successfully.
+			 * @param Data\Domain $domain_before Domain object before.
 			 */
 			do_action( 'darkmatter_domain_updated', $domain_after, $domain_before );
 
 			return $domain_after;
 		}
 
-		return new WP_Error( 'unknown', __( 'Sorry, the domain could not be updated. An unknown error occurred.', 'dark-matter' ) );
+		return new \WP_Error( 'unknown', __( 'Sorry, the domain could not be updated. An unknown error occurred.', 'dark-matter' ) );
 	}
 
 	/**
@@ -877,7 +882,7 @@ private function update_last_changed() {
 	 *
 	 * @since 2.0.0
 	 *
-	 * @return DarkMatter_Domains
+	 * @return Domain
 	 */
 	public static function instance() {
 		static $instance = false;
diff --git a/domain-mapping/api/class-darkmatter-primary.php b/includes/classes/DomainMapping/Manager/Primary.php
similarity index 85%
rename from domain-mapping/api/class-darkmatter-primary.php
rename to includes/classes/DomainMapping/Manager/Primary.php
index 7379ba6d..90d75f1e 100644
--- a/domain-mapping/api/class-darkmatter-primary.php
+++ b/includes/classes/DomainMapping/Manager/Primary.php
@@ -1,21 +1,26 @@
 <?php
 /**
- * Class DarkMatter_Primary
+ * Handles the management of Primary domains.
  *
- * @package DarkMatter
  * @since 2.0.0
+ *
+ * @package DarkMatterPlugin\DomainMapping
  */
 
-defined( 'ABSPATH' ) || die;
+namespace DarkMatter\DomainMapping\Manager;
 
 // phpcs:disable PHPCompatibility.Keywords.ForbiddenNames.unsetFound
 
+use \DarkMatter\DomainMapping\Data;
+
 /**
- * Class DarkMatter_Primary
+ * Class Primary
+ *
+ * Previously called `DarkMatter_Primary`.
  *
  * @since 2.0.0
  */
-class DarkMatter_Primary {
+class Primary {
 	/**
 	 * The Domain Mapping table name for use by the various methods.
 	 *
@@ -60,8 +65,8 @@ public function __construct() {
 	 *
 	 * @since 2.0.0
 	 *
-	 * @param  integer $site_id Site ID to retrieve the primary domain for.
-	 * @return DM_Domain|boolean          Returns the DM_Domain object on success. False otherwise.
+	 * @param int $site_id Site ID to retrieve the primary domain for.
+	 * @return Data\Domain|boolean Returns the DM_Domain object on success. False otherwise.
 	 */
 	public function get( $site_id = 0 ) {
 		$site_id = ( empty( $site_id ) ? get_current_blog_id() : $site_id );
@@ -107,7 +112,7 @@ public function get( $site_id = 0 ) {
 		/**
 		 * Retrieve the entire Domain object.
 		 */
-		$db      = DarkMatter_Domains::instance();
+		$db      = Domain::instance();
 		$_domain = $db->get( $primary_domain );
 
 		return $_domain;
@@ -118,7 +123,7 @@ public function get( $site_id = 0 ) {
 	 *
 	 * @since 2.0.0
 	 *
-	 * @return array Array of DM_Domain objects of the Primary domains for each Site in the Network.
+	 * @return array Array of Domain objects of the Primary domains for each Site in the Network.
 	 */
 	public function get_all() {
 		global $wpdb;
@@ -130,7 +135,7 @@ public function get_all() {
 			return array();
 		}
 
-		$db = DarkMatter_Domains::instance();
+		$db = Domain::instance();
 
 		/**
 		 * Retrieve the DM_Domain objects for each of the primary domains.
@@ -154,13 +159,13 @@ public function get_all() {
 	 * @return boolean True on success, false otherwise.
 	 */
 	public function set( $site_id = 0, $domain = '' ) {
-		$new_primary_domain = DarkMatter_Domains::instance()->get( $domain );
+		$new_primary_domain = Domain::instance()->get( $domain );
 
 		if ( $new_primary_domain->blog_id !== $site_id ) {
 			return false;
 		}
 
-		$result = DarkMatter_Domains::instance()->update(
+		$result = Domain::instance()->update(
 			$new_primary_domain->domain,
 			true,
 			$new_primary_domain->is_https,
@@ -188,13 +193,13 @@ public function set( $site_id = 0, $domain = '' ) {
 	 * @return boolean          True on success. False otherwise.
 	 */
 	public function unset( $site_id = 0, $domain = '', $db = false ) {
-		$new_primary_domain = DarkMatter_Domains::instance()->get( $domain );
+		$new_primary_domain = Domain::instance()->get( $domain );
 
 		if ( $new_primary_domain->blog_id !== $site_id ) {
 			return false;
 		}
 
-		$result = DarkMatter_Domains::instance()->update(
+		$result = Domain::instance()->update(
 			$new_primary_domain->domain,
 			false,
 			$new_primary_domain->is_https,
@@ -226,7 +231,7 @@ private function update_last_changed() {
 	 *
 	 * @since 2.0.0
 	 *
-	 * @return DarkMatter_Primary
+	 * @return Primary
 	 */
 	public static function instance() {
 		static $instance = false;
diff --git a/domain-mapping/api/class-darkmatter-restrict.php b/includes/classes/DomainMapping/Manager/Restricted.php
similarity index 72%
rename from domain-mapping/api/class-darkmatter-restrict.php
rename to includes/classes/DomainMapping/Manager/Restricted.php
index 5b8ee87e..9b0408a1 100644
--- a/domain-mapping/api/class-darkmatter-restrict.php
+++ b/includes/classes/DomainMapping/Manager/Restricted.php
@@ -1,19 +1,22 @@
 <?php
 /**
- * Class DarkMatter_Restrict
+ * Manager for Restricted domains.
  *
- * @package DarkMatter
  * @since 2.0.0
+ *
+ * @package DarkMatterPlugin\DomainMapping
  */
 
-defined( 'ABSPATH' ) || die;
+namespace DarkMatter\DomainMapping\Manager;
 
 /**
- * Class DarkMatter_Restrict
+ * Class Restricted
+ *
+ * Previously called `DarkMatter_Restrict`.
  *
  * @since 2.0.0
  */
-class DarkMatter_Restrict {
+class Restricted {
 	/**
 	 * Restrict table name for database operations.
 	 *
@@ -39,11 +42,11 @@ public function __construct() {
 	 * @since 2.0.0
 	 *
 	 * @param  string $fqdn Fully qualified domain name.
-	 * @return WP_Error|boolean       True on pass. WP_Error on failure.
+	 * @return \WP_Error|boolean       True on pass. WP_Error on failure.
 	 */
 	private function _basic_checks( $fqdn ) {
 		if ( empty( $fqdn ) ) {
-			return new WP_Error( 'empty', __( 'Please include a fully qualified domain name to be added.', 'dark-matter' ) );
+			return new \WP_Error( 'empty', __( 'Please include a fully qualified domain name to be added.', 'dark-matter' ) );
 		}
 
 		/**
@@ -51,26 +54,26 @@ private function _basic_checks( $fqdn ) {
 		 * with a double forward slash.
 		 */
 		if ( false === stripos( $fqdn, '//' ) ) {
-            // phpcs:ignore WordPress.WP.AlternativeFunctions.parse_url_parse_url
+			// phpcs:ignore WordPress.WP.AlternativeFunctions.parse_url_parse_url
 			$domain_parts = parse_url( '//' . ltrim( $fqdn, '/' ) );
 		} else {
-            // phpcs:ignore WordPress.WP.AlternativeFunctions.parse_url_parse_url
+			// phpcs:ignore WordPress.WP.AlternativeFunctions.parse_url_parse_url
 			$domain_parts = parse_url( $fqdn );
 		}
 
 		if ( ! empty( $domain_parts['path'] ) || ! empty( $domain_parts['port'] ) || ! empty( $domain_parts['query'] ) ) {
-			return new WP_Error( 'unsure', __( 'The domain provided contains path, port, or query string information. Please removed this before continuing.', 'dark-matter' ) );
+			return new \WP_Error( 'unsure', __( 'The domain provided contains path, port, or query string information. Please removed this before continuing.', 'dark-matter' ) );
 		}
 
 		$fqdn = $domain_parts['host'];
 
 		if ( defined( 'DOMAIN_CURRENT_SITE' ) && DOMAIN_CURRENT_SITE === $fqdn ) {
-			return new WP_Error( 'wp-config', __( 'You cannot configure the WordPress Network primary domain.', 'dark-matter' ) );
+			return new \WP_Error( 'wp-config', __( 'You cannot configure the WordPress Network primary domain.', 'dark-matter' ) );
 		}
 
-		$domains = DarkMatter_Domains::instance();
+		$domains = Domain::instance();
 		if ( $domains->is_exist( $fqdn ) ) {
-			return new WP_Error( 'used', __( 'This domain is in use.', 'dark-matter' ) );
+			return new \WP_Error( 'used', __( 'This domain is in use.', 'dark-matter' ) );
 		}
 
 		return $fqdn;
@@ -82,7 +85,7 @@ private function _basic_checks( $fqdn ) {
 	 * @since 2.0.0
 	 *
 	 * @param  string $fqdn Domain to be added to the reserve list.
-	 * @return WP_Error|boolean       True on success, WP_Error otherwise.
+	 * @return \WP_Error|boolean       True on success, WP_Error otherwise.
 	 */
 	public function add( $fqdn = '' ) {
 		$fqdn = $this->_basic_checks( $fqdn );
@@ -92,7 +95,7 @@ public function add( $fqdn = '' ) {
 		}
 
 		if ( $this->is_exist( $fqdn ) ) {
-			return new WP_Error( 'exists', __( 'The Domain is already Restricted.', 'dark-matter' ) );
+			return new \WP_Error( 'exists', __( 'The Domain is already Restricted.', 'dark-matter' ) );
 		}
 
 		/**
@@ -100,8 +103,8 @@ public function add( $fqdn = '' ) {
 		 */
 		global $wpdb;
 
-        // phpcs:ignore
-        $result = $wpdb->insert(
+		// phpcs:ignore
+		$result = $wpdb->insert(
 			$this->restrict_table,
 			array(
 				'domain' => $fqdn,
@@ -110,7 +113,7 @@ public function add( $fqdn = '' ) {
 		);
 
 		if ( ! $result ) {
-			return new WP_Error( 'unknown', __( 'An unknown error has occurred. The domain has not been removed from the Restrict list.', 'dark-matter' ) );
+			return new \WP_Error( 'unknown', __( 'An unknown error has occurred. The domain has not been removed from the Restrict list.', 'dark-matter' ) );
 		}
 
 		$this->refresh_cache();
@@ -133,7 +136,7 @@ public function add( $fqdn = '' ) {
 	 * @since 2.0.0
 	 *
 	 * @param  string $fqdn Domain to be deleted to the restrict list.
-	 * @return WP_Error|boolean       True on success, WP_Error otherwise.
+	 * @return \WP_Error|boolean       True on success, WP_Error otherwise.
 	 */
 	public function delete( $fqdn = '' ) {
 		$fqdn = $this->_basic_checks( $fqdn );
@@ -143,7 +146,7 @@ public function delete( $fqdn = '' ) {
 		}
 
 		if ( ! $this->is_exist( $fqdn ) ) {
-			return new WP_Error( 'missing', __( 'The Domain is not found in the Restrict list.', 'dark-matter' ) );
+			return new \WP_Error( 'missing', __( 'The Domain is not found in the Restrict list.', 'dark-matter' ) );
 		}
 
 		/**
@@ -151,8 +154,8 @@ public function delete( $fqdn = '' ) {
 		 */
 		global $wpdb;
 
-        // phpcs:ignore
-        $result = $wpdb->delete(
+		// phpcs:ignore
+		$result = $wpdb->delete(
 			$this->restrict_table,
 			array(
 				'domain' => $fqdn,
@@ -161,7 +164,7 @@ public function delete( $fqdn = '' ) {
 		);
 
 		if ( ! $result ) {
-			return new WP_Error( 'unknown', __( 'An unknown error has occurred. The domain has not been removed from the Restrict list.', 'dark-matter' ) );
+			return new \WP_Error( 'unknown', __( 'An unknown error has occurred. The domain has not been removed from the Restrict list.', 'dark-matter' ) );
 		}
 
 		$this->refresh_cache();
@@ -211,8 +214,8 @@ public function get() {
 		 */
 		global $wpdb;
 
-        // phpcs:ignore
-        $restricted_domains = $wpdb->get_col( "SELECT domain FROM {$this->restrict_table} ORDER BY domain" );
+		// phpcs:ignore
+		$restricted_domains = $wpdb->get_col( "SELECT domain FROM {$this->restrict_table} ORDER BY domain" );
 
 		if ( empty( $restricted_domains ) ) {
 			$restricted_domains = array();
@@ -263,7 +266,7 @@ public function refresh_cache() {
 	 *
 	 * @since 2.0.0
 	 *
-	 * @return DarkMatter_Restrict
+	 * @return Restricted
 	 */
 	public static function instance() {
 		static $instance = false;
diff --git a/domain-mapping/classes/class-dm-url.php b/includes/classes/DomainMapping/Processor/Mapping.php
similarity index 77%
rename from domain-mapping/classes/class-dm-url.php
rename to includes/classes/DomainMapping/Processor/Mapping.php
index 7d714fda..8f2c89b5 100644
--- a/domain-mapping/classes/class-dm-url.php
+++ b/includes/classes/DomainMapping/Processor/Mapping.php
@@ -1,19 +1,27 @@
 <?php
 /**
- * Class DM_URL
+ * Handles the mapping of URLs.
  *
- * @package DarkMatter
  * @since 2.0.0
+ *
+ * @package DarkMatterPlugin\DomainMapping
  */
 
-defined( 'ABSPATH' ) || die();
+namespace DarkMatter\DomainMapping\Processor;
+
+use DarkMatter\DomainMapping\Helper;
+use DarkMatter\DomainMapping\Manager\Domain;
+use DarkMatter\DomainMapping\Manager\Primary;
+use DarkMatter\Interfaces\Registerable;
 
 /**
- * Class DM_URL
+ * Class Mapping
+ *
+ * Previously called `DM_URL`.
  *
  * @since 2.0.0
  */
-class DM_URL {
+class Mapping implements Registerable {
 	/**
 	 * Determine if the current request was mapped in `sunrise.php`.
 	 *
@@ -21,22 +29,22 @@ class DM_URL {
 	 *
 	 * @var bool
 	 */
-	public $is_request_mapped = false;
+	public static $is_request_mapped = false;
 
 	/**
-	 * Constructor.
+	 * Register the hooks and actions.
 	 *
-	 * @since 2.0.0
+	 * @since 3.0.0
 	 */
-	public function __construct() {
-		$this->is_request_mapped = ( defined( 'DOMAIN_MAPPING' ) && DOMAIN_MAPPING );
+	public function register() {
+		self::$is_request_mapped = ( defined( 'DOMAIN_MAPPING' ) && DOMAIN_MAPPING );
 
 		/**
 		 * In some circumstances, we always want to process the logic regardless of request type, circumstances,
 		 * conditions, etc. (like ensuring saved post data is unmapped properly).
 		 */
-		add_filter( 'http_request_host_is_external', array( $this, 'is_external' ), 10, 2 );
-		add_filter( 'wp_insert_post_data', array( $this, 'insert_post' ), -10, 1 );
+		add_filter( 'http_request_host_is_external', [ $this, 'is_external' ], 10, 2 );
+		add_filter( 'wp_insert_post_data', [ $this, 'insert_post' ], -10, 1 );
 
 		/**
 		 * Ensure we do not map on the login and register pages.
@@ -45,7 +53,7 @@ public function __construct() {
 			'wp-login.php'    => true,
 			'wp-register.php' => true,
 		];
-		$filename        = $this->get_request_filename();
+		$filename        = Helper::instance()->get_request_filename();
 		if ( ! empty( $filename ) && array_key_exists( $filename, $admin_filenames ) ) {
 			/**
 			 * Ensure the "Go to [site name]" and Privacy Policy links still go to the mapped domain.
@@ -85,8 +93,7 @@ public function __construct() {
 		 * archived or deleted.
 		 */
 		$blog = get_site();
-
-		if ( (int) $blog->public < 0 || '0' !== $blog->archived || '0' !== $blog->deleted ) {
+		if ( ! Helper::instance()->is_public( $blog ) ) {
 			return;
 		}
 
@@ -97,13 +104,13 @@ public function __construct() {
 		 * the unmapped and mapped domain - like REST API and XMLRPC - will not
 		 * be properly detected for the rewrite rules.
 		 */
-		add_action( 'muplugins_loaded', array( $this, 'prepare' ), -10 );
+		add_action( 'muplugins_loaded', [ $this, 'prepare' ], -10 );
 
 		/**
 		 * Jetpack compatibility. This filter ensures that Jetpack gets the
 		 * correct domain for the home URL.
 		 */
-		add_action( 'jetpack_sync_home_url', array( $this, 'map' ), 10, 1 );
+		add_action( 'jetpack_sync_home_url', [ $this, 'map' ], 10, 1 );
 	}
 
 	/**
@@ -131,10 +138,10 @@ public function adminurl( $url = '', $path = '', $blog_id = 0 ) {
 			return $url;
 		}
 
-		$valid_paths = array(
+		$valid_paths = [
 			'admin-ajax.php' => true,
 			'admin-post.php' => true,
-		);
+		];
 
 		if ( array_key_exists( $filename, $valid_paths ) ) {
 			return $this->map( $url, $blog_id );
@@ -143,22 +150,6 @@ public function adminurl( $url = '', $path = '', $blog_id = 0 ) {
 		return $url;
 	}
 
-	/**
-	 * Get the filename, if it has one, from the current request.
-	 *
-	 * @return string
-	 */
-	public function get_request_filename() {
-		$request_uri = ( empty( $_SERVER['REQUEST_URI'] ) ? '' : wp_unslash( wp_strip_all_tags( $_SERVER['REQUEST_URI'] ) ) );
-		$request     = ltrim( $request_uri, '/' );
-
-		/**
-		 * Get the filename and remove any query strings.
-		 */
-		$filename = basename( $request );
-		return strtok( $filename, '?' );
-	}
-
 	/**
 	 * Checks to ensure that "mapped" domains are considered internal to WordPress and not external.
 	 *
@@ -181,7 +172,7 @@ public function is_external( $external = false, $host = '' ) {
 		 * Attempt to find the domain in Dark Matter. If the domain is found, then tell WordPress it is an internal
 		 * domain.
 		 */
-		$db     = DarkMatter_Domains::instance();
+		$db     = Domain::instance();
 		$domain = $db->find( $host );
 
 		if ( is_a( $domain, 'DM_Domain' ) ) {
@@ -226,8 +217,8 @@ private function is_mapped() {
 		 * the context can be mapped (i.e. it has an active primary domain) and if so, we say the request is mapped.
 		 */
 		global $switched;
-		if ( $switched && $this->is_request_mapped ) {
-			$primary = DarkMatter_Primary::instance()->get();
+		if ( $switched && self::$is_request_mapped ) {
+			$primary = Primary::instance()->get();
 
 			/**
 			 * If there is no primary or if it is inactive, then the site is not mapped.
@@ -239,7 +230,7 @@ private function is_mapped() {
 			return true;
 		}
 
-		return $this->is_request_mapped;
+		return self::$is_request_mapped;
 	}
 
 	/**
@@ -253,32 +244,7 @@ private function is_mapped() {
 	 * @return string           If unmapped URL is found, then returns the primary URL. Untouched otherwise.
 	 */
 	public function map( $value = '', $blog_id = 0 ) {
-		/**
-		 * Ensure that we are working with a string.
-		 */
-		if ( ! is_string( $value ) ) {
-			return $value;
-		}
-
-		/**
-		 * Retrieve the current blog.
-		 */
-		$blog    = get_site( absint( $blog_id ) );
-		$primary = DarkMatter_Primary::instance()->get( $blog->blog_id );
-
-		$unmapped = untrailingslashit( $blog->domain . $blog->path );
-
-		/**
-		 * If there is no primary domain or the unmapped version cannot be found
-		 * then we return the value as-is.
-		 */
-		if ( empty( $primary ) || false === stripos( $value, $unmapped ) ) {
-			return $value;
-		}
-
-		$domain = 'http' . ( $primary->is_https ? 's' : '' ) . '://' . $primary->domain;
-
-		return preg_replace( "#https?://{$unmapped}#", $domain, $value );
+		return Helper::instance()->map( $value, $blog_id );
 	}
 
 	/**
@@ -301,14 +267,14 @@ public function prepare() {
 		 * manipulating `post_content`, usually on the "normal" priority (10). For domain mapping, we want to ensure we
 		 * catch every thing after WordPress core and any plugins, so we run later in the process to achieve that.
 		 */
-		add_filter( 'the_content', array( $this, 'map' ), 5, 1 );
+		add_filter( 'the_content', [ $this, 'map' ], 5, 1 );
 
 		/**
 		 * Please note: the `$this->map()` method will check for unmapped URLs before committing to an regex replace. So
 		 * most of the time, this will go "nothing to do here". And the rest of time, catch any edge cases that produce
 		 * unmapped URLs.
 		 */
-		add_filter( 'the_content', array( $this, 'map' ), 50, 1 );
+		add_filter( 'the_content', [ $this, 'map' ], 50, 1 );
 
 		/**
 		 * We only wish to affect `the_content` for Previews and nothing else.
@@ -334,7 +300,7 @@ public function prepare() {
 		 * action is always called here and not just when the request is called (as in previous versions of Dark
 		 * Matter).
 		 */
-		add_action( 'rest_api_init', array( $this, 'prepare_rest' ) );
+		add_action( 'rest_api_init', [ $this, 'prepare_rest' ] );
 
 		/**
 		 * We have to stop here for the REST API as the later filters and hooks can cause the REST API endpoints to 404
@@ -345,7 +311,7 @@ public function prepare() {
 		}
 
 		if ( is_admin() ) {
-			add_action( 'init', array( $this, 'prepare_admin' ) );
+			add_action( 'init', [ $this, 'prepare_admin' ] );
 			return;
 		}
 
@@ -353,16 +319,16 @@ public function prepare() {
 		 * Every thing here is designed to ensure all URLs throughout WordPress
 		 * is consistent. This is the public serving / theme powered code.
 		 */
-		add_filter( 'admin_url', array( $this, 'adminurl' ), -10, 3 );
-		add_filter( 'home_url', array( $this, 'siteurl' ), -10, 4 );
-		add_filter( 'site_url', array( $this, 'siteurl' ), -10, 4 );
-		add_filter( 'content_url', array( $this, 'map' ), -10, 1 );
-		add_filter( 'get_shortlink', array( $this, 'map' ), -10, 4 );
+		add_filter( 'admin_url', [ $this, 'adminurl' ], -10, 3 );
+		add_filter( 'home_url', [ $this, 'siteurl' ], -10, 4 );
+		add_filter( 'site_url', [ $this, 'siteurl' ], -10, 4 );
+		add_filter( 'content_url', [ $this, 'map' ], -10, 1 );
+		add_filter( 'get_shortlink', [ $this, 'map' ], -10, 4 );
 
-		add_filter( 'script_loader_tag', array( $this, 'map' ), -10, 4 );
-		add_filter( 'style_loader_tag', array( $this, 'map' ), -10, 4 );
+		add_filter( 'script_loader_tag', [ $this, 'map' ], -10, 4 );
+		add_filter( 'style_loader_tag', [ $this, 'map' ], -10, 4 );
 
-		add_filter( 'upload_dir', array( $this, 'upload' ), 10, 1 );
+		add_filter( 'upload_dir', [ $this, 'upload' ], 10, 1 );
 	}
 
 	/**
@@ -375,7 +341,7 @@ public function prepare() {
 	 * @return void
 	 */
 	public function prepare_admin() {
-		add_filter( 'home_url', array( $this, 'siteurl' ), -10, 4 );
+		add_filter( 'home_url', [ $this, 'siteurl' ], -10, 4 );
 
 		/**
 		 * The Preview link in the metabox of Post Publish cannot be handled by the home_url hook. This is because it
@@ -384,13 +350,13 @@ public function prepare_admin() {
 		 * @link https://github.com/WordPress/WordPress/blob/5.2.2/wp-admin/includes/meta-boxes.php#L57 Preview Metabox call to get Preview URL.
 		 * @link https://github.com/WordPress/WordPress/blob/5.2.2/wp-includes/link-template.php#L1311-L1312 Query string parameter "preview=true" being added to the URL.
 		 */
-		add_filter( 'preview_post_link', array( $this, 'unmap' ), 10, 1 );
+		add_filter( 'preview_post_link', [ $this, 'unmap' ], 10, 1 );
 
 		/**
 		 * To prepare the Classic Editor, we need to attach to a very late hook to ensure that `get_current_screen()` is
 		 * available and returns something useful.
 		 */
-		add_action( 'edit_form_top', array( $this, 'prepare_classic_editor' ) );
+		add_action( 'edit_form_top', [ $this, 'prepare_classic_editor' ] );
 	}
 
 	/**
@@ -401,7 +367,7 @@ public function prepare_classic_editor() {
 		$screen = get_current_screen();
 
 		if ( is_a( $screen, 'WP_Screen' ) && 'post' === $screen->base && 'edit' === $screen->parent_base ) {
-			add_filter( 'the_editor_content', array( $this, 'map' ), 10, 1 );
+			add_filter( 'the_editor_content', [ $this, 'map' ], 10, 1 );
 		}
 	}
 
@@ -413,9 +379,9 @@ public function prepare_classic_editor() {
 	 * @return void
 	 */
 	public function prepare_rest() {
-		add_filter( 'home_url', array( $this, 'siteurl' ), -10, 4 );
+		add_filter( 'home_url', [ $this, 'siteurl' ], -10, 4 );
 
-		add_filter( 'preview_post_link', array( $this, 'unmap' ), 10, 1 );
+		add_filter( 'preview_post_link', [ $this, 'unmap' ], 10, 1 );
 
 		/**
 		 * Loop all post types with REST endpoints to fix the mapping for content.raw property.
@@ -423,7 +389,7 @@ public function prepare_rest() {
 		$rest_post_types = get_post_types( [ 'show_in_rest' => true ] );
 
 		foreach ( $rest_post_types as $post_type ) {
-			add_filter( "rest_prepare_{$post_type}", array( $this, 'prepare_rest_post_item' ), 10, 1 );
+			add_filter( "rest_prepare_{$post_type}", [ $this, 'prepare_rest_post_item' ], 10, 1 );
 		}
 	}
 
@@ -431,8 +397,8 @@ public function prepare_rest() {
 	 * Ensures the "raw" version of the content, typically used by Gutenberg through it's middleware pre-load / JS
 	 * hydrate process, gets handled the same as content (which runs through the `the_content` hook).
 	 *
-	 * @param  WP_REST_Response $item Individual post / item in the response that is being processed.
-	 * @return WP_REST_Response       Post / item with the content.raw, if present, mapped.
+	 * @param  \WP_REST_Response $item Individual post / item in the response that is being processed.
+	 * @return \WP_REST_Response       Post / item with the content.raw, if present, mapped.
 	 */
 	public function prepare_rest_post_item( $item = null ) {
 		if ( isset( $item->data['content']['raw'] ) ) {
@@ -463,10 +429,10 @@ public function siteurl( $url = '', $path = '', $scheme = null, $blog_id = 0 ) {
 			return $url;
 		}
 
-		$valid_schemes = array(
+		$valid_schemes = [
 			'http'  => true,
 			'https' => true,
-		);
+		];
 
 		if ( ! is_admin() ) {
 			$valid_schemes['json'] = true;
@@ -527,30 +493,7 @@ public function siteurl( $url = '', $path = '', $scheme = null, $blog_id = 0 ) {
 	 * @return mixed        If unmapped URL is found, then returns the primary URL. Untouched otherwise.
 	 */
 	public function unmap( $value = '' ) {
-		/**
-		 * Ensure that we are working with a string.
-		 */
-		if ( ! is_string( $value ) ) {
-			return $value;
-		}
-
-		/**
-		 * Retrieve the current blog.
-		 */
-		$blog    = get_site();
-		$primary = DarkMatter_Primary::instance()->get();
-
-		/**
-		 * If there is no primary domain or the primary domain cannot be found
-		 * then we return the value as-is.
-		 */
-		if ( empty( $primary ) || false === stripos( $value, $primary->domain ) ) {
-			return $value;
-		}
-
-		$unmapped = 'http' . ( $primary->is_https ? 's' : '' ) . '://' . untrailingslashit( $blog->domain . $blog->path );
-
-		return preg_replace( "#https?://{$primary->domain}#", $unmapped, $value );
+		return Helper::instance()->unmap( $value );
 	}
 
 	/**
@@ -572,22 +515,4 @@ public function upload( $uploads ) {
 
 		return $uploads;
 	}
-
-	/**
-	 * Return the Singleton Instance of the class.
-	 *
-	 * @since 2.0.0
-	 *
-	 * @return DM_URL
-	 */
-	public static function instance() {
-		static $instance = false;
-
-		if ( ! $instance ) {
-			$instance = new self();
-		}
-
-		return $instance;
-	}
 }
-DM_URL::instance();
diff --git a/domain-mapping/classes/class-dm-media.php b/includes/classes/DomainMapping/Processor/Media.php
similarity index 88%
rename from domain-mapping/classes/class-dm-media.php
rename to includes/classes/DomainMapping/Processor/Media.php
index 706b9bc5..2ae652d4 100644
--- a/domain-mapping/classes/class-dm-media.php
+++ b/includes/classes/DomainMapping/Processor/Media.php
@@ -1,20 +1,25 @@
 <?php
 /**
- * Class DM_Media
- *
- * @package DarkMatter
+ * Handles the mapping of media domains.
  *
  * @since 2.2.0
+ *
+ * @package DarkMatterPlugin\DomainMapping
  */
 
-defined( 'ABSPATH' ) || die;
+namespace DarkMatter\DomainMapping\Processor;
+
+use DarkMatter\DomainMapping\Manager\Domain;
+use DarkMatter\DomainMapping\Manager\Primary;
 
 /**
- * Class DM_Media
+ * Class Media
+ *
+ * Previously called `DM_Media`
  *
  * @since 2.2.0
  */
-class DM_Media {
+class Media {
 	/**
 	 * The ID of the current site.
 	 *
@@ -42,13 +47,13 @@ class DM_Media {
 	 * @since 2.2.0
 	 */
 	public function __construct() {
-		add_action( 'init', array( $this, 'init' ), 10 );
-		add_action( 'rest_api_init', array( $this, 'prepare_rest' ) );
-		add_action( 'switch_blog', array( $this, 'switch_blog' ), 10, 1 );
+		add_action( 'init', [ $this, 'init' ], 10 );
+		add_action( 'rest_api_init', [ $this, 'prepare_rest' ] );
+		add_action( 'switch_blog', [ $this, 'switch_blog' ], 10, 1 );
 
-		add_filter( 'the_content', array( $this, 'map' ), 100, 1 );
-		add_filter( 'wp_get_attachment_url', array( $this, 'map_url' ), 100, 1 );
-		add_filter( 'wp_insert_post_data', array( $this, 'insert_post' ), -10, 1 );
+		add_filter( 'the_content', [ $this, 'map' ], 100, 1 );
+		add_filter( 'wp_get_attachment_url', [ $this, 'map_url' ], 100, 1 );
+		add_filter( 'wp_insert_post_data', [ $this, 'insert_post' ], -10, 1 );
 	}
 
 	/**
@@ -86,7 +91,7 @@ private function get_main_domains( $site_id = 0 ) {
 			$unmapped,
 		];
 
-		$primary = DarkMatter_Primary::instance()->get( $site_id );
+		$primary = Primary::instance()->get( $site_id );
 		if ( ! empty( $primary ) ) {
 			$main_domains[] = $primary->domain;
 		}
@@ -295,10 +300,10 @@ public function prepare_rest() {
 		/**
 		 * Loop all post types with REST endpoints to fix the mapping for content.raw property.
 		 */
-		$rest_post_types = get_post_types( array( 'show_in_rest' => true ) );
+		$rest_post_types = get_post_types( [ 'show_in_rest' => true ] );
 
 		foreach ( $rest_post_types as $post_type ) {
-			add_filter( "rest_prepare_{$post_type}", array( $this, 'prepare_rest_post_item' ), 10, 1 );
+			add_filter( "rest_prepare_{$post_type}", [ $this, 'prepare_rest_post_item' ], 10, 1 );
 		}
 	}
 
@@ -306,8 +311,8 @@ public function prepare_rest() {
 	 * Ensures the "raw" version of the content, typically used by Gutenberg through it's middleware pre-load / JS
 	 * hydrate process, gets handled the same as content (which runs through the `the_content` hook).
 	 *
-	 * @param  WP_REST_Response $item Individual post / item in the response that is being processed.
-	 * @return WP_REST_Response       Post / item with the content.raw, if present, mapped.
+	 * @param  \WP_REST_Response $item Individual post / item in the response that is being processed.
+	 * @return \WP_REST_Response       Post / item with the content.raw, if present, mapped.
 	 *
 	 * @since 2.2.0
 	 */
@@ -344,7 +349,7 @@ private function prime_site( $site_id = 0 ) {
 		/**
 		 * Ensure we have media domains to use.
 		 */
-		$media_domains = DarkMatter_Domains::instance()->get_domains_by_type( DM_DOMAIN_TYPE_MEDIA, $site_id );
+		$media_domains = Domain::instance()->get_domains_by_type( DM_DOMAIN_TYPE_MEDIA, $site_id );
 		if ( empty( $media_domains ) ) {
 			$this->sites[ $site_id ] = false;
 			return;
@@ -421,22 +426,4 @@ public function unmap( $value = '' ) {
 			$value
 		);
 	}
-
-	/**
-	 * Return the Singleton Instance of the class.
-	 *
-	 * @return DM_Media
-	 *
-	 * @since 2.2.0
-	 */
-	public static function instance() {
-		static $instance = false;
-
-		if ( ! $instance ) {
-			$instance = new self();
-		}
-
-		return $instance;
-	}
 }
-DM_Media::instance();
diff --git a/includes/classes/DomainMapping/Processor/Redirect.php b/includes/classes/DomainMapping/Processor/Redirect.php
new file mode 100644
index 00000000..3e4bd85f
--- /dev/null
+++ b/includes/classes/DomainMapping/Processor/Redirect.php
@@ -0,0 +1,204 @@
+<?php
+/**
+ * Processor for determining if a redirect is required.
+ *
+ * @since 3.0.0
+ *
+ * @package DarkMatterPlugin\DomainMapping
+ */
+
+namespace DarkMatter\DomainMapping\Processor;
+
+use DarkMatter\DomainMapping\Helper;
+use DarkMatter\DomainMapping\Manager\Primary;
+use DarkMatter\Interfaces\Registerable;
+
+/**
+ * Class Redirect
+ *
+ * @since 3.0.0
+ */
+class Redirect implements Registerable {
+	/**
+	 * Determine if the current request is something we consider for redirecting.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @return bool True to redirect, false otherwise.
+	 */
+	private function can_redirect() {
+		/**
+		 * The function `rest_get_url_prefix()` is not available at this point in the load process. Therefore, we must
+		 * substitute it with a close approximate of what the function does.
+		 *
+		 * There is a side effect of this. Basically if a site is to be setup with a different prefix, in order for this
+		 * to work, the `add_filter()` call would need to be done in a Must-Use Plugin.
+		 *
+		 * @see https://developer.wordpress.org/reference/hooks/rest_url_prefix/
+		 */
+		$rest_url_prefix = '/' . trim( apply_filters( 'rest_url_prefix', 'wp-json' ), '/' ) . '/';
+
+		return ! (
+			/**
+			 * Do not attempt to redirect during the CLI command.
+			 */
+			( defined( 'WP_CLI' ) && WP_CLI )
+			||
+			/**
+			 * AJAX requests can be used on both the mapped and unmapped domains.
+			 */
+			( defined( 'DOING_AJAX' ) && DOING_AJAX )
+			||
+			/**
+			 * Do not attempt to redirect during the execution of cron.
+			 */
+			( defined( 'DOING_CRON' ) && DOING_CRON )
+			||
+			/**
+			 * XMLRPC Requests can be used on both the mapped and unmapped domains.
+			 */
+			( defined( 'XMLRPC_REQUEST' ) && XMLRPC_REQUEST )
+			||
+			/**
+			 * REST API can be used on both the mapped and unmapped domains.
+			 */
+			( ! empty( $_SERVER['REQUEST_URI'] ) && false !== strpos( $_SERVER['REQUEST_URI'], $rest_url_prefix ) ) // phpcs:ignore WordPress.Security.ValidatedSanitizedInput.InputNotSanitized
+			||
+			/**
+			 * Customizer is presented in an <iframe> over the unmapped domain.
+			 */
+			! empty( $_GET['customize_changeset_uuid'] ) // phpcs:ignore WordPress.Security.NonceVerification.Recommended
+			||
+			/**
+			 * Do not redirect Previews
+			 */
+			( ! empty( $_GET['preview'] ) || ! empty( $_GET['page_id'] ) || ! empty( $_GET['p'] ) ) // phpcs:ignore WordPress.Security.NonceVerification.Recommended
+		);
+	}
+
+	/**
+	 * Check to see if the current request is an Admin Post action or an AJAX action. These two requests in Dark Matter
+	 * can be on either the admin domain or the primary domain.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @param string $filename Filename.
+	 * @return bool True if request is AJAX, false otherwise.
+	 */
+	private function is_ajax( $filename = '' ) {
+		$ajax_filenames = [
+			'admin-post.php' => true,
+			'admin-ajax.php' => true,
+		];
+
+
+		if ( ! empty( $filename ) && array_key_exists( $filename, $ajax_filenames ) ) {
+			return true;
+		}
+
+		return false;
+	}
+
+	/**
+	 * Performs various checks and, if required, performs the redirect.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @return void
+	 */
+	public function maybe_redirect() {
+		/**
+		 * Do not perform redirects if it is the main site or the site is _not_ public.
+		 *
+		 * Note: this is here inside the caller on `muplugins_loaded` as earlier is before the function is available for
+		 * use.
+		 */
+		$original_blog = get_site();
+		if ( is_main_site() || ! Helper::instance()->is_public( $original_blog ) ) {
+			return;
+		}
+
+		$filename = Helper::instance()->get_request_filename();
+		if ( $this->is_ajax( $filename ) ) {
+			return;
+		}
+
+		$is_admin = Helper::instance()->is_admin( $filename );
+		$host     = Helper::instance()->get_request_fqdn();
+
+		/**
+		 * Check if logins are allowed on mapped domains, as we shouldn't redirect here if it is allowed.
+		 */
+		if ( ! apply_filters( 'darkmatter_allow_logins', false ) && $is_admin && $host === $original_blog->domain ) {
+			return;
+		}
+
+		/**
+		 * Check we have a primary domain that we can, maybe, redirect to.
+		 */
+		$primary = Primary::instance()->get();
+		if ( ! $primary || ! $primary->active ) {
+			return;
+		}
+
+		/**
+		 * Get the request so we can use it to build up the redirect URL.
+		 */
+		$request_uri = ( empty( $_SERVER['REQUEST_URI'] ) ? '' : filter_var( $_SERVER['REQUEST_URI'], FILTER_SANITIZE_STRING, FILTER_FLAG_STRIP_LOW ) );
+		$request     = ltrim( $request_uri, '/' );
+
+		/**
+		 * Final set of checks. Make sure we redirect were appropriate here, both for the admin side/admin domain and
+		 * the public side/primary domain.
+		 */
+		if ( $is_admin && $host !== $original_blog->domain ) {
+			$is_ssl_admin = ( defined( 'FORCE_SSL_ADMIN' ) && FORCE_SSL_ADMIN );
+
+			$url = 'http' . ( $is_ssl_admin ? 's' : '' ) . '://' . $original_blog->domain . $original_blog->path . $request;
+		} elseif ( $host !== $primary->domain || is_ssl() !== $primary->is_https ) {
+			$url = 'http' . ( $primary->is_https ? 's' : '' ) . '://' . $primary->domain . '/' . $request;
+
+			/**
+			 * Make sure the Path - if this is a sub-folder Network - is removed from the URL. For subdomain Networks,
+			 * the path will be a single forward slash (/).
+			 */
+			if ( '/' !== $original_blog->path ) {
+				$path = '/' . trim( $original_blog->path, '/' ) . '/';
+				$url  = str_ireplace( $path, '/', $url );
+			}
+		}
+
+		/**
+		 * If the URL is empty, then there is no redirect to perform.
+		 */
+		if ( empty( $url ) ) {
+			return;
+		}
+
+		header( 'X-Redirect-By: Dark-Matter-Plugin' );
+		header( 'Location:' . $url, true, 301 );
+
+		die;
+	}
+
+	/**
+	 * Register hooks for this class.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @return void
+	 */
+	public function register() {
+		if ( $this->can_redirect() ) {
+			/**
+			 * We use `muplugins_loaded` action (introduced in WordPress 2.8.0) rather than the "ms_loaded" (introduced
+			 * in WordPress 4.6.0).
+			 *
+			 * A hook on `muplugins_loaded` is used to ensure that WordPress has loaded the Blog/Site globals. This is
+			 * specifically useful when someone goes to the Admin domain URL - http://my.sites.com/two/ - which is to
+			 * redirect to the primary domain - http://example.com.
+			 */
+			add_action( 'muplugins_loaded', [ $this, 'maybe_redirect' ], 20 );
+		}
+	}
+}
diff --git a/domain-mapping/rest/class-dm-rest-domains-controller.php b/includes/classes/DomainMapping/REST/Domains.php
similarity index 70%
rename from domain-mapping/rest/class-dm-rest-domains-controller.php
rename to includes/classes/DomainMapping/REST/Domains.php
index cdfcef5c..e3122385 100644
--- a/domain-mapping/rest/class-dm-rest-domains-controller.php
+++ b/includes/classes/DomainMapping/REST/Domains.php
@@ -1,17 +1,25 @@
 <?php
 /**
- * Class DM_REST_Domains_Controller
+ * REST API for management domains.
  *
- * @package DarkMatter
  * @since 2.0.0
+ *
+ * @package DarkMatterPlugin\DomainMapping
  */
 
+namespace DarkMatter\DomainMapping\REST;
+
+use DarkMatter\DomainMapping\Data;
+use \DarkMatter\DomainMapping\Manager;
+
 /**
- * Class DM_REST_Domains_Controller
+ * Class Domains
+ *
+ * This was previous called `DM_REST_Domains_Controller`.
  *
  * @since 2.0.0
  */
-class DM_REST_Domains_Controller extends WP_REST_Controller {
+class Domains extends \WP_REST_Controller {
 	/**
 	 * Constructor.
 	 *
@@ -28,11 +36,11 @@ public function __construct() {
 	 *
 	 * @since 2.0.0
 	 *
-	 * @param  WP_REST_Request $request Current request.
-	 * @return WP_REST_Response|mixed WP_REST_Response on success. WP_Error on failure.
+	 * @param  \WP_REST_Request $request Current request.
+	 * @return \WP_REST_Response|mixed WP_REST_Response on success. WP_Error on failure.
 	 */
 	public function create_item( $request ) {
-		$db = DarkMatter_Domains::instance();
+		$db = Manager\Domain::instance();
 
 		$item = $this->prepare_item_for_database( $request );
 
@@ -62,7 +70,7 @@ public function create_item( $request ) {
 	 *
 	 * @since 2.0.0
 	 *
-	 * @param  WP_REST_Request $request Current request.
+	 * @param  \WP_REST_Request $request Current request.
 	 * @return boolean True if the current user is a Super Admin. False otherwise.
 	 */
 	public function create_item_permissions_check( $request ) {
@@ -75,11 +83,11 @@ public function create_item_permissions_check( $request ) {
 	 *
 	 * @since 2.0.0
 	 *
-	 * @param  WP_REST_Request $request Current request.
-	 * @return WP_REST_Response|mixed WP_REST_Response on success. WP_Error on failure.
+	 * @param  \WP_REST_Request $request Current request.
+	 * @return \WP_REST_Response|mixed WP_REST_Response on success. WP_Error on failure.
 	 */
 	public function delete_item( $request ) {
-		$db = DarkMatter_Domains::instance();
+		$db = Manager\Domain::instance();
 
 		$result = $db->delete( $request['domain'], $request['force'] );
 
@@ -109,7 +117,7 @@ public function delete_item( $request ) {
 	 *
 	 * @since 2.0.0
 	 *
-	 * @param  WP_REST_Request $request Current request.
+	 * @param  \WP_REST_Request $request Current request.
 	 * @return boolean True if the current user is a Super Admin. False otherwise.
 	 */
 	public function delete_item_permissions_check( $request ) {
@@ -122,11 +130,11 @@ public function delete_item_permissions_check( $request ) {
 	 *
 	 * @since 2.0.0
 	 *
-	 * @param  WP_REST_Request $request Current request.
-	 * @return WP_REST_Response|mixed WP_REST_Response on success. WP_Error on failure.
+	 * @param  \WP_REST_Request $request Current request.
+	 * @return \WP_REST_Response|mixed WP_REST_Response on success. WP_Error on failure.
 	 */
 	public function get_item( $request ) {
-		$db = DarkMatter_Domains::instance();
+		$db = Manager\Domain::instance();
 
 		$result = $db->get( $request['domain'] );
 
@@ -158,136 +166,136 @@ public function get_item_schema() {
 			'$schema'    => 'http://json-schema.org/draft-04/schema#',
 			'title'      => 'Domain',
 			'type'       => 'object',
-			'properties' => array(
-				'id'         => array(
-					'context'     => array( 'view', 'edit' ),
+			'properties' => [
+				'id'         => [
+					'context'     => [ 'view', 'edit' ],
 					'description' => __( 'Unique identifier for the object.', 'dark-matter' ),
 					'readonly'    => true,
 					'type'        => 'integer',
-				),
-				'domain'     => array(
-					'context'     => array( 'view', 'edit' ),
+				],
+				'domain'     => [
+					'context'     => [ 'view', 'edit' ],
 					'default'     => '',
 					'description' => __( 'Domain name.', 'dark-matter' ),
 					'required'    => true,
 					'type'        => 'string',
-				),
-				'is_primary' => array(
-					'context'     => array( 'view', 'edit' ),
+				],
+				'is_primary' => [
+					'context'     => [ 'view', 'edit' ],
 					'default'     => null,
 					'description' => __( 'Domain is the primary domain for the Site.', 'dark-matter' ),
 					'required'    => false,
 					'type'        => 'boolean',
-				),
-				'is_active'  => array(
-					'context'     => array( 'view', 'edit' ),
+				],
+				'is_active'  => [
+					'context'     => [ 'view', 'edit' ],
 					'default'     => null,
 					'description' => __( 'Domain is currently being used.', 'dark-matter' ),
 					'required'    => false,
 					'type'        => 'boolean',
-				),
-				'is_https'   => array(
-					'context'     => array( 'view', 'edit' ),
+				],
+				'is_https'   => [
+					'context'     => [ 'view', 'edit' ],
 					'default'     => null,
 					'description' => __( 'Domain is to be available on the HTTPS protocol.', 'dark-matter' ),
 					'required'    => false,
 					'type'        => 'boolean',
-				),
-				'type'       => array(
-					'context'     => array( 'view', 'edit' ),
+				],
+				'type'       => [
+					'context'     => [ 'view', 'edit' ],
 					'default'     => null,
 					'description' => __( 'Type of domain.', 'dark-matter' ),
 					'required'    => false,
 					'type'        => 'integer',
-				),
-				'site'       => array(
+				],
+				'site'       => [
 					'description' => __( 'Site ID the domain is assigned against.', 'dark-matter' ),
 					'type'        => 'object',
-					'context'     => array( 'view', 'edit' ),
+					'context'     => [ 'view', 'edit' ],
 					'readonly'    => true,
-					'properties'  => array(
-						'blog_id'      => array(
-							'context'     => array( 'view', 'edit' ),
+					'properties'  => [
+						'blog_id'      => [
+							'context'     => [ 'view', 'edit' ],
 							'description' => __( 'Site ID.', 'dark-matter' ),
 							'readonly'    => true,
 							'required'    => false,
 							'type'        => 'integer',
-						),
-						'site_id'      => array(
-							'context'     => array( 'view', 'edit' ),
+						],
+						'site_id'      => [
+							'context'     => [ 'view', 'edit' ],
 							'description' => __( 'The ID of the site\'s parent network.', 'dark-matter' ),
 							'readonly'    => true,
 							'required'    => false,
 							'type'        => 'integer',
-						),
-						'domain'       => array(
-							'context'     => array( 'view', 'edit' ),
+						],
+						'domain'       => [
+							'context'     => [ 'view', 'edit' ],
 							'description' => __( 'Domain of the site.', 'dark-matter' ),
 							'readonly'    => true,
 							'required'    => false,
 							'type'        => 'string',
-						),
-						'path'         => array(
-							'context'     => array( 'view', 'edit' ),
+						],
+						'path'         => [
+							'context'     => [ 'view', 'edit' ],
 							'description' => __( 'Path of the site.', 'dark-matter' ),
 							'readonly'    => true,
 							'required'    => false,
 							'type'        => 'string',
-						),
-						'registered'   => array(
-							'context'     => array( 'view', 'edit' ),
+						],
+						'registered'   => [
+							'context'     => [ 'view', 'edit' ],
 							'description' => __( 'The date on which the site was created or registered.', 'dark-matter' ),
 							'format'      => 'date-time',
 							'readonly'    => true,
 							'required'    => false,
 							'type'        => 'string',
-						),
-						'last_updated' => array(
-							'context'     => array( 'view', 'edit' ),
+						],
+						'last_updated' => [
+							'context'     => [ 'view', 'edit' ],
 							'description' => __( 'The date and time on which site settings were last updated.', 'dark-matter' ),
 							'format'      => 'date-time',
 							'readonly'    => true,
 							'required'    => false,
 							'type'        => 'string',
-						),
-						'public'       => array(
-							'context'     => array( 'view', 'edit' ),
+						],
+						'public'       => [
+							'context'     => [ 'view', 'edit' ],
 							'description' => __( 'Whether the site should be treated as public.', 'dark-matter' ),
 							'readonly'    => true,
 							'required'    => false,
 							'type'        => 'integer',
-						),
-						'archived'     => array(
-							'context'     => array( 'view', 'edit' ),
+						],
+						'archived'     => [
+							'context'     => [ 'view', 'edit' ],
 							'description' => __( 'Whether the site should be treated as archived.', 'dark-matter' ),
 							'readonly'    => true,
 							'required'    => false,
 							'type'        => 'boolean',
-						),
-						'mature'       => array(
-							'context'     => array( 'view', 'edit' ),
+						],
+						'mature'       => [
+							'context'     => [ 'view', 'edit' ],
 							'description' => __( 'Whether the site should be treated as mature.', 'dark-matter' ),
 							'readonly'    => true,
 							'required'    => false,
 							'type'        => 'boolean',
-						),
-						'spam'         => array(
-							'context'     => array( 'view', 'edit' ),
+						],
+						'spam'         => [
+							'context'     => [ 'view', 'edit' ],
 							'description' => __( 'Whether the site should be treated as spam.', 'dark-matter' ),
 							'readonly'    => true,
 							'required'    => false,
 							'type'        => 'boolean',
-						),
-						'deleted'      => array(
-							'context'     => array( 'view', 'edit' ),
+						],
+						'deleted'      => [
+							'context'     => [ 'view', 'edit' ],
 							'description' => __( 'Whether the site should be treated as deleted.', 'dark-matter' ),
 							'readonly'    => true,
 							'required'    => false,
 							'type'        => 'boolean',
-						),
-					),
-				),
-			),
+						],
+					],
+				],
+			],
 		);
 
 		return $schema;
@@ -298,8 +306,8 @@ public function get_item_schema() {
 	 *
 	 * @since 2.0.0
 	 *
-	 * @param  WP_REST_Request $request Current request.
-	 * @return WP_REST_Response|mixed WP_REST_Response on success. WP_Error on failure.
+	 * @param  \WP_REST_Request $request Current request.
+	 * @return \WP_REST_Response|mixed WP_REST_Response on success. WP_Error on failure.
 	 */
 	public function get_items( $request ) {
 		$site_id = null;
@@ -316,9 +324,9 @@ public function get_items( $request ) {
 			$site_id = get_current_blog_id();
 		}
 
-		$db = DarkMatter_Domains::instance();
+		$db = Manager\Domain::instance();
 
-		$response = array();
+		$response = [];
 
 		$result = $db->get_domains( $site_id );
 
@@ -345,7 +353,7 @@ public function get_items( $request ) {
 	 *
 	 * @since 2.0.0
 	 *
-	 * @param  WP_REST_Request $request Current request.
+	 * @param  \WP_REST_Request $request Current request.
 	 * @return boolean True if the current user is a Super Admin. False otherwise.
 	 */
 	public function get_items_permissions_check( $request ) {
@@ -358,17 +366,17 @@ public function get_items_permissions_check( $request ) {
 	 *
 	 * @since 2.0.0
 	 *
-	 * @param  WP_REST_Request $request Current request.
+	 * @param  \WP_REST_Request $request Current request.
 	 * @return array Data provided by the call to the endpoint.
 	 */
 	protected function prepare_item_for_database( $request ) {
-		$item = array(
+		$item = [
 			'domain'     => '',
 			'is_primary' => null,
 			'is_https'   => null,
 			'is_active'  => null,
 			'type'       => null,
-		);
+		];
 
 		$method = $request->get_method();
 
@@ -379,15 +387,15 @@ protected function prepare_item_for_database( $request ) {
 				$value = $request[ $key ];
 			}
 
-			if ( WP_REST_Server::CREATABLE === $method && null === $value && 'is_primary' === $key ) {
+			if ( \WP_REST_Server::CREATABLE === $method && null === $value && 'is_primary' === $key ) {
 				$value = false;
 			}
 
-			if ( WP_REST_Server::CREATABLE === $method && null === $value && 'is_https' === $key ) {
+			if ( \WP_REST_Server::CREATABLE === $method && null === $value && 'is_https' === $key ) {
 				$value = false;
 			}
 
-			if ( WP_REST_Server::CREATABLE === $method && null === $value && 'is_active' === $key ) {
+			if ( \WP_REST_Server::CREATABLE === $method && null === $value && 'is_active' === $key ) {
 				$value = true;
 			}
 
@@ -402,14 +410,14 @@ protected function prepare_item_for_database( $request ) {
 	 *
 	 * @since 2.0.0
 	 *
-	 * @param  DM_Domain       $item Domain object to be prepared for response.
-	 * @param  WP_REST_Request $request Current request.
+	 * @param  Data\Domain      $item    Domain object to be prepared for response.
+	 * @param  \WP_REST_Request $request Current request.
 	 * @return array Prepared item for REST response.
 	 */
 	public function prepare_item_for_response( $item, $request ) {
 		$fields = $this->get_fields_for_response( $request );
 
-		$data = array();
+		$data = [];
 
 		if ( in_array( 'id', $fields, true ) ) {
 			$data['id'] = $item->id;
@@ -479,81 +487,81 @@ public function register_routes() {
 		register_rest_route(
 			$this->namespace,
 			$this->rest_base,
-			array(
-				'methods'             => WP_REST_Server::CREATABLE,
-				'callback'            => array( $this, 'create_item' ),
-				'permission_callback' => array( $this, 'create_item_permissions_check' ),
-				'args'                => $this->get_endpoint_args_for_item_schema( WP_REST_Server::CREATABLE ),
-			)
+			[
+				'methods'             => \WP_REST_Server::CREATABLE,
+				'callback'            => [ $this, 'create_item' ],
+				'permission_callback' => [ $this, 'create_item_permissions_check' ],
+				'args'                => $this->get_endpoint_args_for_item_schema( \WP_REST_Server::CREATABLE ),
+			]
 		);
 
 		register_rest_route(
 			$this->namespace,
 			$this->rest_base . '/(?P<domain>.+)',
-			array(
-				'args' => array(
-					'domain' => array(
+			[
+				'args' => [
+					'domain' => [
 						'description' => __( 'Site ID to retrieve a list of Domains.', 'dark-matter' ),
 						'required'    => true,
 						'type'        => 'string',
-					),
-				),
-				array(
-					'methods'             => WP_REST_Server::READABLE,
-					'callback'            => array( $this, 'get_item' ),
-					'permission_callback' => array( $this, 'get_items_permissions_check' ),
-					'schema'              => array( $this, 'get_item_schema' ),
-				),
-				array(
-					'methods'             => WP_REST_Server::DELETABLE,
-					'callback'            => array( $this, 'delete_item' ),
-					'permission_callback' => array( $this, 'delete_item_permissions_check' ),
-					'args'                => array(
-						'force' => array(
+					],
+				],
+				[
+					'methods'             => \WP_REST_Server::READABLE,
+					'callback'            => [ $this, 'get_item' ],
+					'permission_callback' => [ $this, 'get_items_permissions_check' ],
+					'schema'              => [ $this, 'get_item_schema' ],
+				],
+				[
+					'methods'             => \WP_REST_Server::DELETABLE,
+					'callback'            => [ $this, 'delete_item' ],
+					'permission_callback' => [ $this, 'delete_item_permissions_check' ],
+					'args'                => [
+						'force' => [
 							'default'     => false,
 							'description' => __( 'Force Dark Matter to remove the domain. This is required if you wish to remove a Primary domain from a Site.', 'dark-matter' ),
 							'type'        => 'boolean',
-						),
-					),
-				),
-				array(
-					'methods'             => WP_REST_Server::EDITABLE,
-					'callback'            => array( $this, 'update_item' ),
-					'permission_callback' => array( $this, 'update_item_permissions_check' ),
-					'args'                => $this->get_endpoint_args_for_item_schema( WP_REST_Server::CREATABLE ),
-				),
-			)
+						],
+					],
+				],
+				[
+					'methods'             => \WP_REST_Server::EDITABLE,
+					'callback'            => [ $this, 'update_item' ],
+					'permission_callback' => [ $this, 'update_item_permissions_check' ],
+					'args'                => $this->get_endpoint_args_for_item_schema( \WP_REST_Server::CREATABLE ),
+				],
+			]
 		);
 
 		register_rest_route(
 			$this->namespace,
 			$this->rest_base_plural,
-			array(
-				'methods'             => WP_REST_Server::READABLE,
-				'callback'            => array( $this, 'get_items' ),
-				'permission_callback' => array( $this, 'get_items_permissions_check' ),
-				'schema'              => array( $this, 'get_item_schema' ),
-			)
+			[
+				'methods'             => \WP_REST_Server::READABLE,
+				'callback'            => [ $this, 'get_items' ],
+				'permission_callback' => [ $this, 'get_items_permissions_check' ],
+				'schema'              => [ $this, 'get_item_schema' ],
+			]
 		);
 
 		register_rest_route(
 			$this->namespace,
 			$this->rest_base_plural . '/(?P<site_id>[\d]+)',
-			array(
-				'args' => array(
-					'site_id' => array(
+			[
+				'args' => [
+					'site_id' => [
 						'description' => __( 'Site ID to retrieve a list of Domains.', 'dark-matter' ),
 						'required'    => true,
 						'type'        => 'integer',
-					),
-				),
-				array(
-					'methods'             => WP_REST_Server::READABLE,
-					'callback'            => array( $this, 'get_items' ),
-					'permission_callback' => array( $this, 'get_items_permissions_check' ),
-					'schema'              => array( $this, 'get_item_schema' ),
-				),
-			)
+					],
+				],
+				[
+					'methods'             => \WP_REST_Server::READABLE,
+					'callback'            => [ $this, 'get_items' ],
+					'permission_callback' => [ $this, 'get_items_permissions_check' ],
+					'schema'              => [ $this, 'get_item_schema' ],
+				],
+			]
 		);
 	}
 
@@ -562,11 +570,11 @@ public function register_routes() {
 	 *
 	 * @since 2.0.0
 	 *
-	 * @param  WP_REST_Request $request Current request.
-	 * @return WP_REST_Response|mixed WP_REST_Response on success. WP_Error on failure.
+	 * @param  \WP_REST_Request $request Current request.
+	 * @return \WP_REST_Response|mixed WP_REST_Response on success. WP_Error on failure.
 	 */
 	public function update_item( $request ) {
-		$db = DarkMatter_Domains::instance();
+		$db = Manager\Domain::instance();
 
 		$item = $this->prepare_item_for_database( $request );
 
@@ -601,7 +609,7 @@ public function update_item( $request ) {
 	 *
 	 * @since 2.0.0
 	 *
-	 * @param  WP_REST_Request $request Current request.
+	 * @param  \WP_REST_Request $request Current request.
 	 * @return boolean True if the current user is a Super Admin. False otherwise.
 	 */
 	public function update_item_permissions_check( $request ) {
@@ -609,16 +617,3 @@ public function update_item_permissions_check( $request ) {
 		return current_user_can( apply_filters( 'dark_matter_domain_permission', 'upgrade_network', 'rest-update' ) );
 	}
 }
-
-/**
- * Setup the REST Controller for Domains for use.
- *
- * @since 2.0.0
- *
- * @return void
- */
-function dark_matter_domains_rest() {
-	$controller = new DM_REST_Domains_Controller();
-	$controller->register_routes();
-}
-add_action( 'rest_api_init', 'dark_matter_domains_rest' );
diff --git a/domain-mapping/rest/class-dm-rest-restricted-controller.php b/includes/classes/DomainMapping/REST/Restricted.php
similarity index 66%
rename from domain-mapping/rest/class-dm-rest-restricted-controller.php
rename to includes/classes/DomainMapping/REST/Restricted.php
index 6d53e812..0d94ed1b 100644
--- a/domain-mapping/rest/class-dm-rest-restricted-controller.php
+++ b/includes/classes/DomainMapping/REST/Restricted.php
@@ -1,17 +1,24 @@
 <?php
 /**
- * Class DM_REST_Restricted_Controller
+ * REST API for management of Restricted domains.
  *
- * @package DarkMatter
  * @since 2.0.0
+ *
+ * @package DarkMatterPlugin\DomainMapping
  */
 
+namespace DarkMatter\DomainMapping\REST;
+
+use \DarkMatter\DomainMapping\Manager;
+
 /**
- * Class DM_REST_Restricted_Controller
+ * Class Restricted
+ *
+ * This was previously called `DM_REST_Restricted_Controller`.
  *
  * @since 2.0.0
  */
-class DM_REST_Restricted_Controller extends WP_REST_Controller {
+class Restricted extends \WP_REST_Controller {
 	/**
 	 * Constructor.
 	 *
@@ -27,11 +34,11 @@ public function __construct() {
 	 *
 	 * @since 2.0.0
 	 *
-	 * @param  WP_REST_Request $request Current request.
-	 * @return WP_REST_Response|mixed WP_REST_Response on success. WP_Error on failure.
+	 * @param  \WP_REST_Request $request Current request.
+	 * @return \WP_REST_Response|mixed WP_REST_Response on success. WP_Error on failure.
 	 */
 	public function create_item( $request ) {
-		$db = DarkMatter_Restrict::instance();
+		$db = Manager\Restricted::instance();
 
 		$domain = ( isset( $request['domain'] ) ? $request['domain'] : '' );
 
@@ -46,9 +53,9 @@ public function create_item( $request ) {
 		}
 
 		$response = rest_ensure_response(
-			array(
+			[
 				'domain' => $domain,
-			)
+			]
 		);
 
 		$response->set_status( '201' );
@@ -61,7 +68,7 @@ public function create_item( $request ) {
 	 *
 	 * @since 2.0.0
 	 *
-	 * @param  WP_REST_Request $request Current request.
+	 * @param  \WP_REST_Request $request Current request.
 	 * @return boolean True if the current user is a Super Admin. False otherwise.
 	 */
 	public function create_item_permissions_check( $request ) {
@@ -81,11 +88,11 @@ public function create_item_permissions_check( $request ) {
 	 *
 	 * @since 2.0.0
 	 *
-	 * @param  WP_REST_Request $request Current request.
-	 * @return WP_REST_Response|mixed WP_REST_Response on success. WP_Error on failure.
+	 * @param  \WP_REST_Request $request Current request.
+	 * @return \WP_REST_Response|mixed WP_REST_Response on success. WP_Error on failure.
 	 */
 	public function delete_item( $request ) {
-		$db = DarkMatter_Restrict::instance();
+		$db = Manager\Restricted::instance();
 
 		$domain = ( isset( $request['domain'] ) ? $request['domain'] : '' );
 
@@ -100,10 +107,10 @@ public function delete_item( $request ) {
 		}
 
 		return rest_ensure_response(
-			array(
+			[
 				'deleted' => true,
 				'domain'  => $domain,
-			)
+			]
 		);
 	}
 
@@ -112,7 +119,7 @@ public function delete_item( $request ) {
 	 *
 	 * @since 2.0.0
 	 *
-	 * @param  WP_REST_Request $request Current request.
+	 * @param  \WP_REST_Request $request Current request.
 	 * @return boolean True if the current user is a Super Admin. False otherwise.
 	 */
 	public function delete_item_permissions_check( $request ) {
@@ -125,11 +132,11 @@ public function delete_item_permissions_check( $request ) {
 	 *
 	 * @since 2.0.0
 	 *
-	 * @param  WP_REST_Request $request Current request.
-	 * @return WP_REST_Response|mixed WP_REST_Response on success. WP_Error on failure.
+	 * @param  \WP_REST_Request $request Current request.
+	 * @return \WP_REST_Response|mixed WP_REST_Response on success. WP_Error on failure.
 	 */
 	public function get_items( $request ) {
-		$db = DarkMatter_Restrict::instance();
+		$db = Manager\Restricted::instance();
 
 		return rest_ensure_response( $db->get() );
 	}
@@ -140,7 +147,7 @@ public function get_items( $request ) {
 	 *
 	 * @since 2.0.0
 	 *
-	 * @param  WP_REST_Request $request Current request.
+	 * @param  \WP_REST_Request $request Current request.
 	 * @return boolean True if the current user is a Super Admin. False otherwise.
 	 */
 	public function get_items_permissions_check( $request ) {
@@ -160,9 +167,9 @@ public function register_routes() {
 			$this->namespace,
 			$this->rest_base,
 			[
-				'methods'             => WP_REST_Server::CREATABLE,
-				'callback'            => array( $this, 'create_item' ),
-				'permission_callback' => array( $this, 'create_item_permissions_check' ),
+				'methods'             => \WP_REST_Server::CREATABLE,
+				'callback'            => [ $this, 'create_item' ],
+				'permission_callback' => [ $this, 'create_item_permissions_check' ],
 			]
 		);
 
@@ -170,9 +177,9 @@ public function register_routes() {
 			$this->namespace,
 			$this->rest_base,
 			[
-				'methods'             => WP_REST_Server::DELETABLE,
-				'callback'            => array( $this, 'delete_item' ),
-				'permission_callback' => array( $this, 'delete_item_permissions_check' ),
+				'methods'             => \WP_REST_Server::DELETABLE,
+				'callback'            => [ $this, 'delete_item' ],
+				'permission_callback' => [ $this, 'delete_item_permissions_check' ],
 			]
 		);
 
@@ -180,23 +187,10 @@ public function register_routes() {
 			$this->namespace,
 			$this->rest_base,
 			[
-				'methods'             => WP_REST_Server::READABLE,
-				'callback'            => array( $this, 'get_items' ),
-				'permission_callback' => array( $this, 'get_items_permissions_check' ),
+				'methods'             => \WP_REST_Server::READABLE,
+				'callback'            => [ $this, 'get_items' ],
+				'permission_callback' => [ $this, 'get_items_permissions_check' ],
 			]
 		);
 	}
 }
-
-/**
- * Setup the REST Controller for Domains for use.
- *
- * @since 2.0.0
- *
- * @return void
- */
-function dark_matter_restricted_rest() {
-	$controller = new DM_REST_Restricted_Controller();
-	$controller->register_routes();
-}
-add_action( 'rest_api_init', 'dark_matter_restricted_rest' );
diff --git a/includes/classes/DomainMapping/Sunrise.php b/includes/classes/DomainMapping/Sunrise.php
new file mode 100644
index 00000000..41876ee1
--- /dev/null
+++ b/includes/classes/DomainMapping/Sunrise.php
@@ -0,0 +1,143 @@
+<?php
+/**
+ * Handles the logic for WordPress dropin plugin, `sunrise.php`.
+ *
+ * @since 3.0.0
+ *
+ * @package DarkMatterPlugin\DomainMapping
+ *
+ * @phpcs:disable WordPress.WP.GlobalVariablesOverride.Prohibited
+ */
+
+namespace DarkMatter\DomainMapping;
+
+use DarkMatter\DomainMapping\Data;
+use DarkMatter\DomainMapping\Manager;
+use DarkMatter\DomainMapping\Processor\Redirect;
+
+/**
+ * Class Sunrise
+ *
+ * @since 3.0.0
+ */
+class Sunrise {
+	/**
+	 * Constructor.
+	 *
+	 * @since 3.0.0
+	 */
+	public function __construct() {
+		$this->init();
+
+		/**
+		 * Find the domain based on the request.
+		 */
+		$domain = $this->get_domain();
+		if ( $domain && $domain->active && $this->set_globals( $domain ) && $domain->is_primary ) {
+			$this->update_globals( $domain );
+		}
+
+		/**
+		 * Hook up the redirect logic.
+		 */
+		$redirect = new Redirect();
+		$redirect->register();
+	}
+
+	/**
+	 * Get the domain from the requested FQDN.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @return bool|Data\Domain
+	 */
+	private function get_domain() {
+		$fqdn = Helper::instance()->get_request_fqdn();
+		return Manager\Domain::instance()->get( $fqdn );
+	}
+
+	/**
+	 * Set up various globals and constants which are used, either by Dark Matter itself or by other plugins and/or
+	 * WordPress Core.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @return void
+	 */
+	private function init() {
+		/**
+		 * Ensure `dark-matter` cache group is available globally.
+		 */
+		wp_cache_add_global_groups( 'dark-matter' );
+
+		/**
+		 * Define the `SUNRISE_LOADED`. Dark Matter Plugin does not make use of this but other plugins do in certain
+		 * circumstances (i.e. Jetpack). So we define it for compatibility.
+		 */
+		if ( false === defined( 'SUNRISE_LOADED' ) ) {
+			define( 'SUNRISE_LOADED', true );
+		}
+
+		/**
+		 * Use to detect misconfiguration where the cookie domain is set.
+		 */
+		define( 'DARKMATTER_COOKIE_SET', ! defined( 'COOKIE_DOMAIN' ) );
+	}
+
+	/**
+	 * Sets up a few global variables which are used through WordPress Core. Will do some basic detection to ensure the
+	 * website should be served on the mapped domain.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @param Data\Domain $domain Domain data.
+	 * @return bool True to proceed, false to disengage.
+	 */
+	private function set_globals( $domain ) {
+		global $blog_id, $current_blog, $current_site, $site_id;
+
+		/**
+		 * Set the current Blog (WP_Site) and current Site (WP_Network).
+		 */
+		$current_blog = get_site( $domain->blog_id );
+		$blog_id      = $current_blog->blog_id;
+		$current_site = \WP_Network::get_instance( $current_blog->site_id );
+		$site_id      = $current_blog->site_id;
+
+		return Helper::instance()->is_public( $current_blog );
+	}
+
+	/**
+	 * Prepare WordPress globals to use the primary domain data instead.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @param Data\Domain $primary Primary Domain data.
+	 * @return void
+	 */
+	private function update_globals( $primary ) {
+		/**
+		 * Store the current WP_Site object in another global, so it is available for comparison and reference.
+		 */
+		global $current_blog, $original_blog;
+		$original_blog = clone $current_blog;
+
+		/**
+		 * Update the domain and path to match the primary.
+		 */
+		$current_blog->domain = $primary->domain;
+		$current_blog->path   = '/';
+
+		/**
+		 * Update the cookie domain to be the primary domain.
+		 */
+		if ( ! defined( 'COOKIE_DOMAIN' ) ) {
+			define( 'COOKIE_DOMAIN', $primary->domain );
+		}
+
+		/**
+		 * Set the constant to state the current request has been mapped.
+		 */
+		define( 'DOMAIN_MAPPING', true );
+	}
+}
diff --git a/domain-mapping/classes/third-party/class-dm-yoast.php b/includes/classes/DomainMapping/Support/Yoast.php
similarity index 69%
rename from domain-mapping/classes/third-party/class-dm-yoast.php
rename to includes/classes/DomainMapping/Support/Yoast.php
index a6acdf21..e5a0bca4 100644
--- a/domain-mapping/classes/third-party/class-dm-yoast.php
+++ b/includes/classes/DomainMapping/Support/Yoast.php
@@ -2,32 +2,32 @@
 /**
  * Compatibility adjustments for supporting Yoast SEO.
  *
- * @package DarkMatter
+ * @since 2.1.3
+ *
+ * @package DarkMatterPlugin\DomainMapping
  */
 
+namespace DarkMatter\DomainMapping\Support;
+
+use DarkMatter\DomainMapping\Helper;
+use DarkMatter\Interfaces\Registerable;
+
 /**
- * Class DM_Yoast
+ * Class Yoast
+ *
+ * Previously called `DM_Yoast`.
  *
  * @since 2.1.3
  */
-class DM_Yoast {
-	/**
-	 * DM_Yoast constructor.
-	 */
-	public function __construct() {
-		if ( defined( 'WPSEO_VERSION' ) ) {
-			return;
-		}
-
-		add_filter( 'wpseo_should_save_indexable', [ $this, 'fix_indexable_permalinks' ], 10, 2 );
-	}
-
+class Yoast implements Registerable {
 	/**
 	 * Correct indexables permalinks to be unmapped prior to save to the database. This works with versions 15.1+ of
 	 * Yoast SEO. Version 15.1 - which contains the `wpseo_should_save_indexable` was released on 14th October 2020.
 	 *
 	 * @link https://github.com/Yoast/wordpress-seo/blob/15.1/src/builders/indexable-builder.php#L296
 	 *
+	 * @since 2.1.3
+	 *
 	 * @param boolean                        $intend_to_save Whether the indexable is to be saved or not.
 	 * @param \Yoast\WP\SEO\Models\Indexable $indexable The indexable to be saved.
 	 * @return boolean The default value of "intend to save".
@@ -37,15 +37,18 @@ public function fix_indexable_permalinks( $intend_to_save, $indexable ) {
 		 * If saving to the database, then make sure the permalink is unmapped.
 		 */
 		if ( $intend_to_save ) {
-			$dm_url               = DM_URL::instance();
-			$indexable->permalink = $dm_url->unmap( $indexable->permalink );
+			$indexable->permalink = Helper::instance()->unmap( $indexable->permalink );
 		}
 
 		return $intend_to_save;
 	}
-}
 
-/**
- * Only instantiate this class if Yoast SEO is in use.
- */
-new DM_Yoast();
+	/**
+	 * Register hooks for this class.
+	 *
+	 * @return void
+	 */
+	public function register() {
+		add_filter( 'wpseo_should_save_indexable', [ $this, 'fix_indexable_permalinks' ], 10, 2 );
+	}
+}
diff --git a/includes/classes/Interfaces/Registerable.php b/includes/classes/Interfaces/Registerable.php
new file mode 100644
index 00000000..21bb137e
--- /dev/null
+++ b/includes/classes/Interfaces/Registerable.php
@@ -0,0 +1,22 @@
+<?php
+/**
+ * Useful interface for making registerable classes consistent.
+ *
+ * @package DarkMatter
+ */
+
+namespace DarkMatter\Interfaces;
+
+/**
+ * Interface Registerable
+ *
+ * @since 3.0.0
+ */
+interface Registerable {
+	/**
+	 * Register method for connecting with actions and filters.
+	 *
+	 * @return void
+	 */
+	public function register();
+}
diff --git a/includes/classes/SSO/Admin.php b/includes/classes/SSO/Admin.php
new file mode 100644
index 00000000..2fe7c1a2
--- /dev/null
+++ b/includes/classes/SSO/Admin.php
@@ -0,0 +1,52 @@
+<?php
+/**
+ * Provides single sign-on action links with the admin UI for admins / editors.
+ *
+ * @package DarkMatterPlugin\SSO
+ */
+
+namespace DarkMatter\SSO;
+
+use DarkMatter\Interfaces\Registerable;
+
+/**
+ * Class Admin
+ */
+class Admin implements Registerable {
+	/**
+	 * Add an option to log in to the site on the admin bar.
+	 *
+	 * @param \WP_Admin_Bar $admin_bar Admin bar object.
+	 * @return \WP_Admin_Bar
+	 */
+	public function admin_bar( $admin_bar ) {
+		if ( ! $admin_bar instanceof \WP_Admin_Bar ) {
+			return $admin_bar;
+		}
+
+		$check_url = Authorise::get_check_url();
+		if ( empty( $check_url ) ) {
+			return $admin_bar;
+		}
+
+		$admin_bar->add_node(
+			[
+				'id'     => 'dark-matter-plugin-signin',
+				'href'   => $check_url,
+				'parent' => 'site-name',
+				'title'  => __( 'Log into Site', 'dark-matter-plugin' ),
+			]
+		);
+
+		return $admin_bar;
+	}
+
+	/**
+	 * Handle actions and filters for the SSO admin.
+	 *
+	 * @return void
+	 */
+	public function register() {
+		add_action( 'admin_bar_menu', [ $this, 'admin_bar' ], 40 );
+	}
+}
diff --git a/includes/classes/SSO/Authenticate.php b/includes/classes/SSO/Authenticate.php
new file mode 100644
index 00000000..c8169bf7
--- /dev/null
+++ b/includes/classes/SSO/Authenticate.php
@@ -0,0 +1,208 @@
+<?php
+/**
+ * Authentication for SSO.
+ *
+ * @package DarkMatterPlugin\SSO
+ */
+
+namespace DarkMatter\SSO;
+
+use DarkMatter\Interfaces\Registerable;
+use function DarkMatter\Functions\verify_nonce;
+
+/**
+ * Class Authenticate
+ */
+class Authenticate implements Registerable {
+	/**
+	 * Token API.
+	 *
+	 * @var null|Token
+	 */
+	private $token_api = null;
+
+	/**
+	 * Constructor.
+	 */
+	public function __construct() {
+		$this->token_api = new Token( 'dmp_login_token', 'dark-matter-plugin-logintoken' );
+	}
+
+	/**
+	 * Retrieve the URL data.
+	 *
+	 * @return array|false|null
+	 */
+	private function get_data() {
+		return filter_var_array(
+			$_GET,
+			[
+				'action' => [
+					'filter'  => FILTER_CALLBACK,
+					'options' => 'sanitize_text_field',
+				],
+				'nonce'  => [
+					'filter'  => FILTER_CALLBACK,
+					'options' => 'sanitize_text_field',
+				],
+				'token'  => [
+					'filter'  => FILTER_CALLBACK,
+					'options' => 'sanitize_text_field',
+				],
+				'key'    => [
+					'filter'  => FILTER_CALLBACK,
+					'options' => 'sanitize_key',
+				],
+			]
+		);
+	}
+
+	/**
+	 * Prepare a redirect to the mapped domain which can be used for authentication and log on.
+	 *
+	 * @param string $token_id   Token ID.
+	 * @param array  $token_data Data from the Token that completed the authorisation.
+	 * @return void
+	 */
+	public function prepare( $token_id, $token_data ) {
+		if ( ! is_user_logged_in() ) {
+			return;
+		}
+
+		$user_id = get_current_user_id();
+		$nonce   = wp_create_nonce( sprintf( 'dmp_login_check_%s', $user_id ) );
+
+		/**
+		 * Generate a random key.
+		 */
+		$key = wp_hash( $user_id . wp_rand() . microtime(), 'dmp_authenticate' );
+
+		$data = [
+			'key'     => $key,
+			'nonce'   => $nonce,
+			'user_id' => $user_id,
+		];
+
+		/**
+		 * Hashed the key and store it. This will be used to cross-reference later.
+		 */
+		$hashed_key = wp_hash( wp_json_encode( $data ), 'dmp_authenticate' );
+		$data['key'] = $hashed_key;
+
+		/**
+		 * Now add the session token. As this data is a bit more sensitive, we only want to store this in the within the
+		 * Cache API/Token logic but not include it in the one-way hash for the URL.
+		 */
+		$data['session_token'] = wp_get_session_token();
+
+		// Create a new token with User ID in the data.
+		$token_id = $this->token_api->create( $user_id, '', $data );
+
+		$url = add_query_arg(
+			[
+				'action' => 'dmp_auth_do',
+				'token'  => $token_id,
+				'nonce'  => $nonce,
+				'key'    => $key,
+				't'      => time(), // Cache buster
+			],
+			home_url( '/' )
+		);
+
+		// Redirect to the mapped domain to log them in.
+		wp_safe_redirect( $url, 302, 'DarkMatterPlugin' );
+		die;
+	}
+
+	/**
+	 * Handle actions and filters for SSO Authenticate.
+	 *
+	 * @return void
+	 */
+	public function register() {
+		add_action( 'darkmatterplugin.sso.authorised', [ $this, 'prepare' ], 10, 2 );
+
+		// Add action to log in the user.
+		add_action( 'template_redirect', [ $this, 'signin' ] ); // TODO: Should probably be a custom action from DMP when a mapped request has been determined.
+	}
+
+	/**
+	 * Perform sign-in request.
+	 *
+	 * @return void
+	 */
+	public function signin() {
+		$data = $this->get_data();
+
+		if ( 'dmp_auth_do' !== $data['action'] ) {
+			return;
+		}
+
+		/**
+		 * Check to see if the token exists.
+		 */
+		$token_data = $this->token_api->get( $data['token'], 'token' );
+		if ( empty( $token_data['nonce'] ) && empty( $token_data['user_id'] ) ) {
+			return;
+		}
+
+		/**
+		 * Check the nonce matches.
+		 */
+		if ( $data['nonce'] !== $token_data['nonce'] ) {
+			return;
+		}
+
+		/**
+		 * Check the key hash and make sure it is valid.
+		 */
+		$unverified_key = wp_hash(
+			wp_json_encode(
+				[
+					'key'     => $data['key'],
+					'nonce'   => $data['nonce'],
+					'user_id' => $token_data['user_id'],
+				]
+			),
+			'dmp_authenticate'
+		);
+
+		$hashes_match = $unverified_key && hash_equals( $token_data['key'], $unverified_key );
+		if ( ! $hashes_match ) {
+			return;
+		}
+
+		wp_set_auth_cookie( $token_data['user_id'], false, '', $token_data['session_token'] );
+		wp_set_current_user( $token_data['user_id'] );
+
+		/**
+		 * `wp_verify_nonce()` works with `$_COOKIE` to retrieve the auth cookies and despite being set above, the auth
+		 * cookies are not available in this manner. This means the retrieving the current WP User and get the session
+		 * token does not work, meaning the nonce always fails.
+		 *
+		 * The below allows us to perform the check with the need for `$_COOKIE` being updated.
+		 */
+		$verify_nonce = verify_nonce(
+			$token_data['nonce'],
+			sprintf( 'dmp_login_check_%s', $token_data['user_id'] ),
+			$token_data['user_id'],
+			$token_data['session_token']
+		);
+
+		/**
+		 * With the person signed in, perform an actual verification on the nonce. If it fails, then immediately clear
+		 * the auth cookies.
+		 */
+		if ( ! $verify_nonce ) {
+			/**
+			 * Sadly the `wp_verify_nonce()` does not provide a way to supply the relevant data without the auth cookies
+			 * being set. However, this weird "create" and "destroy" immediately approach to cookies.
+			 */
+			wp_clear_auth_cookie();
+			return;
+		}
+
+		wp_safe_redirect( home_url( '/' ), 302, 'DarkMatterPlugin' );
+		die;
+	}
+}
diff --git a/includes/classes/SSO/Authorise.php b/includes/classes/SSO/Authorise.php
new file mode 100644
index 00000000..dbc8fc51
--- /dev/null
+++ b/includes/classes/SSO/Authorise.php
@@ -0,0 +1,266 @@
+<?php
+/**
+ * Handle the SSO authorisation flow.
+ *
+ * @package DarkMatterPlugin\SSO
+ */
+
+namespace DarkMatter\SSO;
+
+use DarkMatter\Interfaces\Registerable;
+
+/**
+ * Class Authorise
+ */
+class Authorise implements Registerable {
+	/**
+	 * URL data.
+	 *
+	 * @var array
+	 */
+	private $data = [];
+
+	/**
+	 * Token API.
+	 *
+	 * @var null|Token
+	 */
+	private $token_api = null;
+
+	/**
+	 * Constructor.
+	 */
+	public function __construct() {
+		$this->token_api = new Token( 'dmp_auth_token', 'dark-matter-plugin-authtokens', true );
+	}
+
+	/**
+	 * Ensure the admin request is valid.
+	 *
+	 * @return bool True to proceed. False otherwise.
+	 */
+	private function is_valid_admin() {
+		/**
+		 * If they are not logged in, then we ignore it.
+		 */
+		if ( ! is_user_logged_in() ) {
+			return false;
+		}
+
+		/**
+		 * Make sure we are an admin request and that it is
+		 */
+		if ( wp_doing_ajax() || ! is_admin() ) {
+			return false;
+		}
+
+		return true;
+	}
+
+	/**
+	 * Helper method to get the check URL for logging in a person to the primary domain.
+	 *
+	 * @return string
+	 */
+	public static function get_check_url() {
+		$user_id   = get_current_user_id();
+		$token_api = new Token( 'dmp_auth_token', 'dark-matter-plugin-authtokens', true );
+
+		$token_id = $token_api->get( $user_id );
+		if ( empty( $token_id ) ) {
+			return '';
+		}
+
+		$token_data = $token_api->get( $token_id, 'token' );
+		if ( empty( $token_data['nonce'] ) && empty( $token_data['user_id'] ) ) {
+			return '';
+		}
+
+		return add_query_arg(
+			[
+				'action' => 'dmp_auth_check',
+				'token'  => $token_id,
+				'nonce'  => $token_data['nonce'],
+			],
+			home_url( '/' )
+		);
+	}
+
+	/**
+	 * Get the URL data.
+	 *
+	 * @return void
+	 */
+	private function get_data() {
+		$this->data = filter_var_array(
+			$_GET,
+			[
+				'action' => [
+					'filter'  => FILTER_CALLBACK,
+					'options' => 'sanitize_text_field',
+				],
+				'nonce'  => [
+					'filter'  => FILTER_CALLBACK,
+					'options' => 'sanitize_text_field',
+				],
+				'token'  => [
+					'filter'  => FILTER_CALLBACK,
+					'options' => 'sanitize_text_field',
+				],
+			]
+		);
+	}
+
+	/**
+	 * Handle the authorise request.
+	 *
+	 * @return void
+	 */
+	public function handle() {
+		if ( is_user_logged_in() ) {
+			return;
+		}
+
+		/**
+		 * Check to see if the token exists.
+		 */
+		$token_data = $this->token_api->get( $this->data['token'], 'token' );
+		if ( empty( $token_data['nonce'] ) && empty( $token_data['user_id'] ) ) {
+			return;
+		}
+
+		/**
+		 * Check the nonce matches.
+		 */
+		if ( $this->data['nonce'] !== $token_data['nonce'] ) {
+			return;
+		}
+
+		$url = admin_url();
+		$url = add_query_arg(
+			[
+				'action' => 'dmp_auth_verify',
+				'token'  => $this->data['token'],
+				'nonce'  => $this->data['nonce'],
+			],
+			$url
+		);
+
+		wp_safe_redirect( $url, 302, 'Dark-Matter-Plugin' );
+		die;
+	}
+
+	/**
+	 * Initiate the Authorise process by creating a token.
+	 *
+	 * @return void
+	 */
+	public function initiate() {
+		if ( ! $this->is_valid_admin() ) {
+			return;
+		}
+
+		$user_id = get_current_user_id();
+
+		/**
+		 * Check to see if a Token already exists.
+		 */
+		$token = $this->token_api->get( $user_id );
+		if ( ! empty( $token ) ) {
+			return;
+		}
+
+		$data = [
+			'user_id' => $user_id,
+			'nonce'   => wp_create_nonce( sprintf( 'dmp_auth_check_%s', $user_id ) ),
+		];
+
+		$this->token_api->create( $user_id, '', $data );
+	}
+
+	/**
+	 * Handle actions and filters for this SSO Authorise.
+	 *
+	 * @return void
+	 */
+	public function register() {
+		if ( wp_doing_ajax() ) {
+			return;
+		}
+
+		$this->get_data();
+
+		if ( empty( $this->data['action'] ) ) {
+			add_action( 'init', [ $this, 'initiate' ], 11 );
+		}
+
+		/**
+		 * Check if the current request has data and has the action.
+		 */
+		if ( ! empty( $this->data ) && 'dmp_auth_check' === $this->data['action'] ) {
+			add_action( 'template_redirect', [ $this, 'handle' ] ); // TODO: Should probably be a custom action from DMP when a mapped request has been determined.
+		}
+
+		/**
+		 * Verification must only occur on the admin domain (unmapped).
+		 */
+		if (
+			! empty( $this->data )
+			&& ( is_admin() )
+			&& 'dmp_auth_verify' === $this->data['action'] ) {
+			add_action( 'init', [ $this, 'verify' ], 11 );
+		}
+	}
+
+	/**
+	 * Verify a request provided by the handle method.
+	 *
+	 * @return void
+	 */
+	public function verify() {
+		if ( ! $this->is_valid_admin() ) {
+			return;
+		}
+
+		$user_id = get_current_user_id();
+
+		$token_id = $this->token_api->get( $user_id );
+		if ( empty( $token_id ) || $this->data['token'] !== $token_id ) {
+			return;
+		}
+
+		$token_data = $this->token_api->get( $token_id, 'token' );
+		if ( empty( $token_data ) ) {
+			return;
+		}
+
+		/**
+		 * Make sure the Token we are verifying is for the same user as us.
+		 */
+		if ( $token_data['user_id'] !== $user_id ) {
+			return;
+		}
+
+		/**
+		 * Verify the nonce properly now.
+		 *
+		 * As this is processed on the admin domain, the person's session is up and running, which will mean the nonce
+		 * verify is meaningful.
+		 */
+		if ( ! wp_verify_nonce( $token_data['nonce'], sprintf( 'dmp_auth_check_%s', $user_id ) ) ) {
+			return;
+		}
+
+		$this->token_api->delete( $user_id, $token_id );
+
+		/**
+		 * Action that is fired when the SSO is authorised with a crafted URL from the front-end.
+		 *
+		 * @since 3.0.0
+		 *
+		 * @param string $token_id   Token ID.
+		 * @param array  $token_data Data from the Token that completed the authorisation.
+		 */
+		do_action( 'darkmatterplugin.sso.authorised', $token_id, $token_data );
+	}
+}
diff --git a/includes/classes/SSO/Token.php b/includes/classes/SSO/Token.php
new file mode 100644
index 00000000..a5a798da
--- /dev/null
+++ b/includes/classes/SSO/Token.php
@@ -0,0 +1,139 @@
+<?php
+/**
+ * Helper class for the management and storage of tokens.
+ *
+ * @package DarkMatterPlugin\SSO
+ */
+
+namespace DarkMatter\SSO;
+
+/**
+ * Class Token
+ */
+class Token {
+	/**
+	 * Token cache group.
+	 *
+	 * @var string
+	 */
+	private $cache_group = 'dark-matter-plugin-tokens';
+
+	/**
+	 * Token name prefix.
+	 *
+	 * @var string
+	 */
+	private $prefix = '';
+
+	/**
+	 * Constructor.
+	 *
+	 * @param string $prefix       Token prefix.
+	 * @param string $cache_group  Override the cache group.
+	 * @param bool   $cache_global Add the cache group to the global groups, so available across the network.
+	 */
+	public function __construct( $prefix = '', $cache_group = '', $cache_global = false ) {
+		$this->prefix = $prefix ?? 'dmp_token_';
+
+		if ( ! empty( $cache_group ) ) {
+			$this->cache_group = $cache_group;
+		}
+
+		if ( $cache_global ) {
+			wp_cache_add_global_groups( $this->cache_group );
+		}
+	}
+
+	/**
+	 * Create a token.
+	 *
+	 * @param int    $user_id  User ID.
+	 * @param string $token_id Token ID. If blank, will auto-generate.
+	 * @param array  $data     Array of data to store with the token.
+	 * @return false|string Token ID on success. False otherwise.
+	 */
+	public function create( $user_id, $token_id = '', $data = [] ) {
+		if ( ! is_integer( $user_id ) ) {
+			return false;
+		}
+
+		/**
+		 * No Token ID, then generate one.
+		 */
+		if ( empty( $token_id ) ) {
+			$token_id = wp_generate_password( 20, false );
+		}
+
+		/**
+		 * Create an entry so that Token can be found by looking up a WP User ID.
+		 */
+		wp_cache_set( sprintf( '%1$sfor_%2$s', $this->prefix, $user_id ), $token_id, $this->cache_group, HOUR_IN_SECONDS );
+
+		/**
+		 * Create the actual token entry with the appropriate data.
+		 */
+		wp_cache_set( sprintf( '%1$s%2$s', $this->prefix, $token_id ), $data, $this->cache_group, HOUR_IN_SECONDS );
+
+		return $token_id;
+	}
+
+	/**
+	 * Delete a token.
+	 *
+	 * @param int    $user_id  User ID.
+	 * @param string $token_id Token ID.
+	 * @return bool True on success. False otherwise.
+	 */
+	public function delete( $user_id, $token_id ) {
+		if ( is_integer( $user_id ) && ! empty( $token_id ) ) {
+			wp_cache_delete( sprintf( '%1$sfor_%2$s', $this->prefix, $user_id ), $this->cache_group );
+			wp_cache_delete( sprintf( '%1$s%2$s', $this->prefix, $token_id ), $this->cache_group );
+
+			return true;
+		}
+
+		return false;
+	}
+
+	/**
+	 * Retrieve a token by Token ID or User ID.
+	 *
+	 * @param string $id   ID to retrieve token.
+	 * @param string $type ID type; "token" or "user".
+	 * @return false|string|array Data from the Token, either as an array or string. Can return false if cache entry has
+	 *                            been deleted.
+	 */
+	public function get( $id, $type = 'user' ) {
+		$prefix = [
+			'token' => $this->prefix,
+			'user'  => sprintf( '%1$sfor_', $this->prefix ),
+		];
+
+		if ( ! array_key_exists( $type, $prefix ) ) {
+			return [];
+		}
+
+		$key = sprintf( '%1$s%2$s', $prefix[ $type ], $id );
+
+		return wp_cache_get( $key, $this->cache_group );
+	}
+
+	/**
+	 * Update a token.
+	 *
+	 * Note: this will extend the length of time the token will remain.
+	 *
+	 * @param int   $token_id Token ID.
+	 * @param array $data     Data.
+	 * @return bool True on success. False otherwise.
+	 */
+	public function set( $token_id, $data = [] ) {
+		if ( empty( $token_id ) ) {
+			return false;
+		}
+
+		wp_cache_set( sprintf( '%1$s%2$s', $this->prefix, $token_id ), $data, $this->cache_group, HOUR_IN_SECONDS );
+
+		return true;
+	}
+}
diff --git a/includes/classes/UI/AbstractAdminPage.php b/includes/classes/UI/AbstractAdminPage.php
new file mode 100644
index 00000000..7e46988f
--- /dev/null
+++ b/includes/classes/UI/AbstractAdminPage.php
@@ -0,0 +1,125 @@
+<?php
+/**
+ * Helper class for adding admin pages.
+ *
+ * @since 3.0.0
+ * @package DarkMatter
+ */
+
+namespace DarkMatter\UI;
+
+use DarkMatter\Interfaces\Registerable;
+
+/**
+ * Class AbstractAdminPage
+ *
+ * @since 3.0.0
+ */
+abstract class AbstractAdminPage implements Registerable {
+	/**
+	 * Menu Title
+	 *
+	 * @since 3.0.0
+	 *
+	 * @var string
+	 */
+	protected $menu_title = '';
+
+	/**
+	 * Page Title
+	 *
+	 * @since 3.0.0
+	 *
+	 * @var string
+	 */
+	protected $page_title = '';
+
+	/**
+	 * Parent Slug (defaults to "Settings" / `options-general.php`)
+	 *
+	 * @since 3.0.0
+	 *
+	 * @var string
+	 */
+	protected $parent_slug = 'options-general.php';
+
+	/**
+	 * Capability/permission required to view the page.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @var string
+	 */
+	protected $permission = '';
+
+	/**
+	 * Slug
+	 *
+	 * @since 3.0.0
+	 *
+	 * @var string
+	 */
+	protected $slug = '';
+
+	/**
+	 * Add the menu item to the page.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @return void
+	 */
+	public function admin_menu() {
+		$hook_suffix = add_submenu_page(
+			$this->parent_slug,
+			$this->page_title,
+			$this->menu_title,
+			$this->permission,
+			$this->slug,
+			[ $this, 'page' ]
+		);
+
+		add_action( 'load-' . $hook_suffix, [ $this, 'enqueue' ] );
+	}
+
+	/**
+	 * Used for enqueuing custom scripts and styles.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @return void
+	 */
+	abstract public function enqueue();
+
+	/**
+	 * Handle the rendering of the page.
+	 *
+	 * @return void
+	 */
+	public function page() {
+		if ( ! current_user_can( $this->permission ) ) {
+			wp_die( esc_html__( 'You do not have permission to manage domains.', 'dark-matter' ) );
+		}
+
+		$this->render();
+	}
+
+	/**
+	 * Produce the HTML output of the admin page.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @return void
+	 */
+	abstract public function render();
+
+	/**
+	 * Register hooks for this class.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @return void
+	 */
+	public function register() {
+		add_action( 'admin_menu', [ $this, 'admin_menu' ] );
+	}
+}
diff --git a/domain-mapping/sunrise.php b/includes/dropins/sunrise.php
similarity index 64%
rename from domain-mapping/sunrise.php
rename to includes/dropins/sunrise.php
index 64cefb5b..fb478f46 100644
--- a/domain-mapping/sunrise.php
+++ b/includes/dropins/sunrise.php
@@ -14,8 +14,13 @@
  * @package DarkMatter
  */
 
-$sunrise_path = ( dirname( __FILE__ ) . '/plugins/dark-matter/domain-mapping/inc/sunrise.php' );
+$dirname = ( dirname( __FILE__ ) . '/plugins/dark-matter/' );
 
-if ( is_readable( $sunrise_path ) ) {
-	require_once $sunrise_path;
+/**
+ * Include the PSR-4 autoloader.
+ */
+if ( file_exists( $dirname . 'vendor/autoload.php' ) ) {
+	require_once $dirname . 'vendor/autoload.php';
 }
+
+new \DarkMatter\DomainMapping\Sunrise();
diff --git a/includes/utility/functions.php b/includes/utility/functions.php
new file mode 100644
index 00000000..f90f36c8
--- /dev/null
+++ b/includes/utility/functions.php
@@ -0,0 +1,56 @@
+<?php
+/**
+ * Utility functions.
+ *
+ * @package DarkMatterPlugin
+ */
+
+namespace DarkMatter\Functions;
+
+/**
+ * A version of `wp_verify_nonce()` but can be fed a WP User ID and a Session Token, whereas the in-built one relies on
+ * getting the information from session cookies.
+ *
+ * @param string     $nonce   Nonce value that was used for verification, usually via a form field.
+ * @param string|int $action  Should give context to what is taking place and be the same when nonce was created.
+ * @param int        $user_id User ID.
+ * @param string     $token   Session token.
+ * @return int|false
+ */
+function verify_nonce( $nonce, $action = -1, $user_id = 0, $token = '' ) {
+	$nonce = (string) $nonce;
+	$uid   = (int) $user_id;
+
+	if ( empty( $nonce ) || empty( $user_id ) || empty( $token ) ) {
+		return false;
+	}
+
+	$user = get_user_by( 'id', $user_id );
+	if ( ! $user instanceof \WP_User ) {
+		return false;
+	}
+
+	$i = wp_nonce_tick( $action );
+
+	// Nonce generated 0-12 hours ago.
+	$expected = substr( wp_hash( $i . '|' . $action . '|' . $uid . '|' . $token, 'nonce' ), -12, 10 );
+	if ( hash_equals( $expected, $nonce ) ) {
+		return 1;
+	}
+
+	// Nonce generated 12-24 hours ago.
+	$expected = substr( wp_hash( ( $i - 1 ) . '|' . $action . '|' . $uid . '|' . $token, 'nonce' ), -12, 10 );
+	if ( hash_equals( $expected, $nonce ) ) {
+		return 2;
+	}
+
+	/**
+	 * Fires when nonce verification fails.
+	 *
+	 * @see wp_verify_nonce()
+	 */
+	do_action( 'wp_verify_nonce_failed', $nonce, $action, $user, $token );
+
+	// Invalid nonce.
+	return false;
+}
diff --git a/scripts/release.sh b/scripts/release.sh
index 0786bd40..33df62b9 100644
--- a/scripts/release.sh
+++ b/scripts/release.sh
@@ -18,7 +18,6 @@ rm -rf domain-mapping/ui
 rm -rf node_modules
 rm -rf scripts
 rm -rf tests
-rm -rf vendor
 rm -rf .*
 rm *.json
 rm *.lock
diff --git a/tests/phpunit/domain-mapping/DomainsTest.php b/tests/phpunit/domain-mapping/DomainsTest.php
index 14e4f599..ba87960d 100644
--- a/tests/phpunit/domain-mapping/DomainsTest.php
+++ b/tests/phpunit/domain-mapping/DomainsTest.php
@@ -46,7 +46,7 @@ public function setUp() : void {
 	 */
 	public function test_add_domain() {
 		$domain = 'mappeddomain1.test';
-		DarkMatter_Domains::instance()->add( $domain );
+		\DarkMatter\DomainMapping\Manager\Domain::instance()->add( $domain );
 
 		global $wpdb;
 		$data = $wpdb->get_row(
@@ -71,12 +71,12 @@ public function test_add_add_again() {
 		/**
 		 * Add the domain.
 		 */
-		DarkMatter_Domains::instance()->add( $domain );
+		\DarkMatter\DomainMapping\Manager\Domain::instance()->add( $domain );
 
 		/**
 		 * Attempt to add the domain again.
 		 */
-		$error = DarkMatter_Domains::instance()->add( $domain );
+		$error = \DarkMatter\DomainMapping\Manager\Domain::instance()->add( $domain );
 
 		$this->assertWPError( $error );
 		$this->assertSame( $error->get_error_code(), 'exists' );
@@ -93,12 +93,12 @@ public function test_delete_domain() {
 		/**
 		 * Add the domain.
 		 */
-		DarkMatter_Domains::instance()->add( $domain );
+		\DarkMatter\DomainMapping\Manager\Domain::instance()->add( $domain );
 
 		/**
 		 * Attempt to add the domain again.
 		 */
-		$return = DarkMatter_Domains::instance()->delete( $domain );
+		$return = \DarkMatter\DomainMapping\Manager\Domain::instance()->delete( $domain );
 
 		$this->assertTrue( $return );
 
@@ -125,12 +125,12 @@ public function test_find_domain() {
 		/**
 		 * Add the domain.
 		 */
-		DarkMatter_Domains::instance()->add( $domain );
+		\DarkMatter\DomainMapping\Manager\Domain::instance()->add( $domain );
 
 		/**
 		 * Attempt to add the domain again.
 		 */
-		$return = DarkMatter_Domains::instance()->find( $domain );
+		$return = \DarkMatter\DomainMapping\Manager\Domain::instance()->find( $domain );
 
 		$this->assertNotFalse( $return );
 		$this->assertEquals( $return->domain, $domain );
@@ -147,12 +147,12 @@ public function test_update_domain() {
 		/**
 		 * Add the domain.
 		 */
-		DarkMatter_Domains::instance()->add( $domain );
+		\DarkMatter\DomainMapping\Manager\Domain::instance()->add( $domain );
 
 		/**
 		 * Make sure the update did not return a WP_Error.
 		 */
-		$return = DarkMatter_Domains::instance()->update( $domain, true, true );
+		$return = \DarkMatter\DomainMapping\Manager\Domain::instance()->update( $domain, true, true );
 		$this->assertNotWPError( $return );
 
 		/**
@@ -178,12 +178,12 @@ public function test_update_domain() {
 	 */
 	public function test_validation_international_domains() {
 		/** Chinese - Unicode - Invalid */
-		$return = DarkMatter_Domains::instance()->add( 'www.例如.中国' );
+		$return = \DarkMatter\DomainMapping\Manager\Domain::instance()->add( 'www.例如.中国' );
 		$this->assertWPError( $return, 'Chinese - Unicode - Invalid' );
 		$this->assertSame( $return->get_error_code(), 'domain' );
 
 		/** Chinese - ASCII - Valid */
-		$return = DarkMatter_Domains::instance()->add( 'www.xn--fsqu6v.xn--fiqs8s' );
+		$return = \DarkMatter\DomainMapping\Manager\Domain::instance()->add( 'www.xn--fsqu6v.xn--fiqs8s' );
 		$this->assertNotWPError( $return, 'Chinese - ASCII - Valid' );
 	}
 
@@ -194,37 +194,37 @@ public function test_validation_international_domains() {
 	 */
 	public function test_validation_invalid_domains() {
 		/** Empty */
-		$return = DarkMatter_Domains::instance()->add( '' );
+		$return = \DarkMatter\DomainMapping\Manager\Domain::instance()->add( '' );
 		$this->assertWPError( $return );
 		$this->assertSame( $return->get_error_code(), 'empty' );
 
 		/** URI */
-		$return = DarkMatter_Domains::instance()->add( 'http://example.com/' );
+		$return = \DarkMatter\DomainMapping\Manager\Domain::instance()->add( 'http://example.com/' );
 		$this->assertWPError( $return );
 		$this->assertSame( $return->get_error_code(), 'unsure' );
 
 		/** Domain + Path */
-		$return = DarkMatter_Domains::instance()->add( 'example.com/hello-world' );
+		$return = \DarkMatter\DomainMapping\Manager\Domain::instance()->add( 'example.com/hello-world' );
 		$this->assertWPError( $return );
 		$this->assertSame( $return->get_error_code(), 'unsure' );
 
 		/** Domain + Port */
-		$return = DarkMatter_Domains::instance()->add( 'example.com:443' );
+		$return = \DarkMatter\DomainMapping\Manager\Domain::instance()->add( 'example.com:443' );
 		$this->assertWPError( $return );
 		$this->assertSame( $return->get_error_code(), 'unsure' );
 
 		/** DOMAIN_CURRENT_SITE */
-		$return = DarkMatter_Domains::instance()->add( 'darkmatter.test' );
+		$return = \DarkMatter\DomainMapping\Manager\Domain::instance()->add( 'darkmatter.test' );
 		$this->assertWPError( $return );
 		$this->assertSame( $return->get_error_code(), 'wp-config' );
 
 		/** Non-ASCII - i.e. emojis, etc. */
-		$return = DarkMatter_Domains::instance()->add( '🐲' );
+		$return = \DarkMatter\DomainMapping\Manager\Domain::instance()->add( '🐲' );
 		$this->assertWPError( $return );
 		$this->assertSame( $return->get_error_code(), 'domain' );
 
 		/** Stored XSS (and curious input from an administrator one time ... ... ...) */
-		$return = DarkMatter_Domains::instance()->add( '<script>( function ( $ ) { $.ready( () => { console.log( \'hello world\' ); } ); } )( window.jQuery )</script>' );
+		$return = \DarkMatter\DomainMapping\Manager\Domain::instance()->add( '<script>( function ( $ ) { $.ready( () => { console.log( \'hello world\' ); } ); } )( window.jQuery )</script>' );
 		$this->assertWPError( $return );
 		$this->assertSame( $return->get_error_code(), 'unsure' );
 	}
@@ -241,19 +241,19 @@ public function test_validation_valid_domains() {
 		 */
 
 		/** Localhost */
-		$return = DarkMatter_Domains::instance()->add( 'localhost' );
+		$return = \DarkMatter\DomainMapping\Manager\Domain::instance()->add( 'localhost' );
 		$this->assertNotWPError( $return );
 
 		/** Example domain */
-		$return = DarkMatter_Domains::instance()->add( 'example.com' );
+		$return = \DarkMatter\DomainMapping\Manager\Domain::instance()->add( 'example.com' );
 		$this->assertNotWPError( $return );
 
 		/** Example sub-domain */
-		$return = DarkMatter_Domains::instance()->add( 'www.example.com' );
+		$return = \DarkMatter\DomainMapping\Manager\Domain::instance()->add( 'www.example.com' );
 		$this->assertNotWPError( $return );
 
 		/** Atypical test domain. */
-		$return = DarkMatter_Domains::instance()->add( 'development.test' );
+		$return = \DarkMatter\DomainMapping\Manager\Domain::instance()->add( 'development.test' );
 		$this->assertNotWPError( $return );
 	}
 }
diff --git a/tests/phpunit/domain-mapping/MappingDomainsTest.php b/tests/phpunit/domain-mapping/MappingDomainsTest.php
index e6ea9a74..ca85af62 100644
--- a/tests/phpunit/domain-mapping/MappingDomainsTest.php
+++ b/tests/phpunit/domain-mapping/MappingDomainsTest.php
@@ -64,7 +64,7 @@ public function setUp() : void {
 			]
 		);
 
-		DarkMatter_Domains::instance()->network_media = [
+		\DarkMatter\DomainMapping\Manager\Domain::instance()->network_media = [
 			$this->media_domain,
 		];
 
@@ -73,7 +73,7 @@ public function setUp() : void {
 		/**
 		 * Add domains to the new site.
 		 */
-		DarkMatter_Domains::instance()->add(
+		\DarkMatter\DomainMapping\Manager\Domain::instance()->add(
 			$this->primary_domain,
 			true,
 			true
@@ -188,7 +188,7 @@ public function test_logout_url() {
 	 * @return void
 	 */
 	public function test_rest_url() {
-		DM_URL::instance()->is_request_mapped = true;
+		\DarkMatter\DomainMapping\Processor\Mapping::$is_request_mapped = true;
 
 		$this->assertEquals(
 			/**
@@ -199,6 +199,6 @@ public function test_rest_url() {
 			'REST API URL'
 		);
 
-		DM_URL::instance()->is_request_mapped = false;
+		\DarkMatter\DomainMapping\Processor\Mapping::$is_request_mapped = false;
 	}
 }
diff --git a/tests/phpunit/domain-mapping/MediaDomainsTest.php b/tests/phpunit/domain-mapping/MediaDomainsTest.php
index 56c1befb..02b63633 100644
--- a/tests/phpunit/domain-mapping/MediaDomainsTest.php
+++ b/tests/phpunit/domain-mapping/MediaDomainsTest.php
@@ -36,7 +36,7 @@ public function setUp() : void {
 			]
 		);
 	}
-	
+
 	/**
 	 * Media domains set by the `DM_NETWORK_MEDIA` constant.
 	 *
@@ -47,14 +47,14 @@ public function test_get_media_domains_constant() {
 			'cdn1.darkmatter.test',
 		];
 
-		DarkMatter_Domains::instance()->network_media = $constant_domains;
+		\DarkMatter\DomainMapping\Manager\Domain::instance()->network_media = $constant_domains;
 
-		$domains = DarkMatter_Domains::instance()->get_domains_by_type();
+		$domains = \DarkMatter\DomainMapping\Manager\Domain::instance()->get_domains_by_type();
 
 		$expected = [];
 
 		foreach ( $constant_domains as $media_domain ) {
-			$expected[] = new DM_Domain(
+			$expected[] = new \DarkMatter\DomainMapping\Data\Domain(
 				(object) [
 					'active'     => true,
 					'blog_id'    => get_current_blog_id(),
@@ -79,7 +79,7 @@ public function test_get_media_domains_manual() {
 		/**
 		 * Reset any hard-coded media domains.
 		 */
-		DarkMatter_Domains::instance()->network_media = [];
+		\DarkMatter\DomainMapping\Manager\Domain::instance()->network_media = [];
 
 		$media_domains = [
 			'cdn1.mappeddomain1.test' => -1,
@@ -93,7 +93,7 @@ public function test_get_media_domains_manual() {
 		 * Create domains.
 		 */
 		foreach ( $media_domains as $domain => $id ) {
-			$result = DarkMatter_Domains::instance()->add(
+			$result = \DarkMatter\DomainMapping\Manager\Domain::instance()->add(
 				$domain,
 				false,
 				true,
@@ -109,12 +109,12 @@ public function test_get_media_domains_manual() {
 		/**
 		 * Retrieve the domains.
 		 */
-		$domains = DarkMatter_Domains::instance()->get_domains_by_type();
+		$domains = \DarkMatter\DomainMapping\Manager\Domain::instance()->get_domains_by_type();
 
 		$expected = [];
 
 		foreach ( $media_domains as $media_domain => $id ) {
-			$expected[] = new DM_Domain(
+			$expected[] = new \DarkMatter\DomainMapping\Data\Domain(
 				(object) [
 					'active'     => true,
 					'blog_id'    => get_current_blog_id(),
diff --git a/tests/phpunit/domain-mapping/PrimaryDomainTest.php b/tests/phpunit/domain-mapping/PrimaryDomainTest.php
index 36e3ec16..2eb8578b 100644
--- a/tests/phpunit/domain-mapping/PrimaryDomainTest.php
+++ b/tests/phpunit/domain-mapping/PrimaryDomainTest.php
@@ -19,14 +19,14 @@ class PrimaryDomainTest extends \WP_UnitTestCase {
 	/**
 	 * Holder for Domains class.
 	 *
-	 * @var DarkMatter_Domains|null
+	 * @var \DarkMatter\DomainMapping\Manager\Domain|null
 	 */
 	private $darkmatter_domains = null;
 
 	/**
 	 * Holder for Primary class.
 	 *
-	 * @var DarkMatter_Primary|null
+	 * @var \DarkMatter\DomainMapping\Manager\Primary|null
 	 */
 	private $darkmatter_primary = null;
 
@@ -67,8 +67,8 @@ public static function wpTearDownAfterClass() {
 	public function setUp(): void {
 		parent::setUp();
 
-		$this->darkmatter_domains = DarkMatter_Domains::instance();
-		$this->darkmatter_primary = DarkMatter_Primary::instance();
+		$this->darkmatter_domains = \DarkMatter\DomainMapping\Manager\Domain::instance();
+		$this->darkmatter_primary = \DarkMatter\DomainMapping\Manager\Primary::instance();
 
 		switch_to_blog( self::$blog_id );
 	}
diff --git a/tests/phpunit/domain-mapping/RestrictedDomainsTest.php b/tests/phpunit/domain-mapping/RestrictedDomainsTest.php
index afb8937c..a7911165 100644
--- a/tests/phpunit/domain-mapping/RestrictedDomainsTest.php
+++ b/tests/phpunit/domain-mapping/RestrictedDomainsTest.php
@@ -44,7 +44,7 @@ public function setUp() : void {
 	 */
 	public function test_add_restrict_domain() {
 		$domain = 'restricteddomain1.test';
-		$result = DarkMatter_Restrict::instance()->add( $domain );
+		$result = \DarkMatter\DomainMapping\Manager\Restricted::instance()->add( $domain );
 
 		$this->assertTrue( $result, 'Adding a restricted domain.' );
 	}
@@ -60,13 +60,13 @@ public function test_remove_restrict_domain() {
 		/**
 		 * Add domain.
 		 */
-		$result = DarkMatter_Restrict::instance()->add( $domain );
+		$result = \DarkMatter\DomainMapping\Manager\Restricted::instance()->add( $domain );
 		$this->assertTrue( $result, 'Adding a restricted domain.' );
 
 		/**
 		 * Remove domain.
 		 */
-		$result = DarkMatter_Restrict::instance()->delete( $domain );
+		$result = \DarkMatter\DomainMapping\Manager\Restricted::instance()->delete( $domain );
 		$this->assertTrue( $result, 'Removing a restricted domain.' );
 	}
 
@@ -81,7 +81,7 @@ public function test_restrict_domain_add_domain() {
 		/**
 		 * Add domain.
 		 */
-		$result = DarkMatter_Restrict::instance()->add( $domain );
+		$result = \DarkMatter\DomainMapping\Manager\Restricted::instance()->add( $domain );
 		$this->assertTrue( $result, 'Adding a restricted domain.' );
 
 		/**
@@ -89,7 +89,7 @@ public function test_restrict_domain_add_domain() {
 		 */
 		switch_to_blog( $this->blog_id );
 
-		$result = DarkMatter_Domains::instance()->add( $domain );
+		$result = \DarkMatter\DomainMapping\Manager\Domain::instance()->add( $domain );
 		$this->assertWPError( $result, 'WP_Error for adding a restricted domain.' );
 		$this->assertSame( 'reserved', $result->get_error_code(), 'Correct WP_Error for restricted domain.' );
 	}
@@ -103,13 +103,13 @@ public function test_get_restricted_domains() {
 		$domains = [ 'restricteddomain1.test', 'restricteddomain2.test' ];
 
 		foreach ( $domains as $domain ) {
-			$result = DarkMatter_Restrict::instance()->add( $domain );
+			$result = \DarkMatter\DomainMapping\Manager\Restricted::instance()->add( $domain );
 			$this->assertTrue( $result, 'Adding a restricted domain.' );
 		}
 
 		$this->assertSame(
 			$domains,
-			DarkMatter_Restrict::instance()->get(),
+			\DarkMatter\DomainMapping\Manager\Restricted::instance()->get(),
 			'Get returns all the restricted domains properly.'
 		);
 	}