diff --git a/index.js b/index.js
index 4f45b70..46e0cdd 100644
--- a/index.js
+++ b/index.js
@@ -1,5 +1,22 @@
-module.exports = function deepFreeze (o) {
-  Object.freeze(o);
+'use strict';
+module.exports = function deepFreeze (o, method) {
+  if (!method) {
+   var method = 'freeze';
+  }
+
+  function isNotExtensible(o) {
+    return !Object.isExtensible(o);
+  }
+
+  var checkFn;
+  switch (method) {
+    case 'freeze': checkFn = Object.isFrozen; break;
+    case 'seal': checkFn = Object.isSealed; break;
+    case 'preventExtensions': checkFn = isNotExtensible; break;
+    default: throw new TypeError("Method must be 'freeze', 'seal', or 'preventExtensions'");
+  }
+
+  Object[method](o);
 
   var oIsFunction = typeof o === "function";
   var hasOwnProp = Object.prototype.hasOwnProperty;
@@ -9,8 +26,8 @@ module.exports = function deepFreeze (o) {
     && (oIsFunction ? prop !== 'caller' && prop !== 'callee' && prop !== 'arguments' : true )
     && o[prop] !== null
     && (typeof o[prop] === "object" || typeof o[prop] === "function")
-    && !Object.isFrozen(o[prop])) {
-      deepFreeze(o[prop]);
+    && !checkFn(o[prop])) {
+      deepFreeze(o[prop], method);
     }
   });
   
diff --git a/readme.markdown b/readme.markdown
index 378c6ed..cc8df39 100644
--- a/readme.markdown
+++ b/readme.markdown
@@ -42,6 +42,29 @@ var deepFreeze = require('deep-freeze-strict')
 Call `Object.freeze(obj)` recursively on all unfrozen properties of `obj` that
 are functions or objects.
 
+## deepFreeze(obj, 'freeze')
+
+Same as `deepFreeze(obj)`.
+
+## deepFreeze(obj, 'seal')
+
+Call `Object.seal(obj)` recursively on all unsealed properties of `obj` that
+are functions or objects.
+
+## deepFreeze(obj, 'preventExtensions')
+
+Call `Object.preventExtensions(obj)` recursively on all not isExtensible properties of `obj` that
+are functions or objects.
+
+# Freeze, seal, and preventExtensions
+`'preventExtensions'` is the least restrictive. It prevents arbitraty properties from added to an object.
+
+`'seal'` does everything preventExtensions does, and also prevents altering the attributes of the properties on the object, as well as preventing deletion of properties on the object.
+
+`'freeze'` is the most restrictive. It does everything preventExtensions and seal does, as well as making all of the existing properties on the object read-only.
+
+Once an object is frozen (or sealed, or not extensible), it cannot be undone.
+
 # license
 
 public domain
diff --git a/test/freeze.js b/test/freeze.js
new file mode 100644
index 0000000..33f22d8
--- /dev/null
+++ b/test/freeze.js
@@ -0,0 +1,23 @@
+var test = require('tap').test;
+var deepFreeze = require('../');
+
+test('freeze', function (t) {
+  "use strict";
+
+  t.plan(6);
+
+  var a = {
+    // a function
+      b: function() {},
+  };
+
+  deepFreeze(a, 'freeze');
+  t.assert(!Object.isExtensible(a));
+  t.assert(!Object.isExtensible(a.b));
+
+  t.assert(Object.isSealed(a));
+  t.assert(Object.isSealed(a.b));
+  
+  t.assert(Object.isFrozen(a));
+  t.assert(Object.isFrozen(a.b));
+});
\ No newline at end of file
diff --git a/test/preventExtensions.js b/test/preventExtensions.js
new file mode 100644
index 0000000..21fea82
--- /dev/null
+++ b/test/preventExtensions.js
@@ -0,0 +1,23 @@
+var test = require('tap').test;
+var deepFreeze = require('../');
+
+test('preventExtensions', function (t) {
+  "use strict";
+
+  t.plan(6);
+
+  var a = {
+    // a function
+      b: function() {},
+  };
+
+  deepFreeze(a, 'preventExtensions');
+  t.assert(!Object.isExtensible(a));
+  t.assert(!Object.isExtensible(a.b));
+
+  t.assert(!Object.isSealed(a));
+  t.assert(Object.isSealed(a.b));
+  
+  t.assert(!Object.isFrozen(a));
+  t.assert(!Object.isFrozen(a.b)); 
+});
diff --git a/test/seal.js b/test/seal.js
new file mode 100644
index 0000000..7b47787
--- /dev/null
+++ b/test/seal.js
@@ -0,0 +1,23 @@
+var test = require('tap').test;
+var deepFreeze = require('../');
+
+test('seal', function (t) {
+  "use strict";
+
+  t.plan(6);
+
+  var a = {
+    // a function
+      b: function() {},
+  };
+
+  deepFreeze(a, 'seal');
+  t.assert(!Object.isExtensible(a));
+  t.assert(!Object.isExtensible(a.b));
+
+  t.assert(Object.isSealed(a));
+  t.assert(Object.isSealed(a.b));
+  
+  t.assert(!Object.isFrozen(a));
+  t.assert(!Object.isFrozen(a.b));
+});
\ No newline at end of file
diff --git a/test/type.js b/test/type.js
new file mode 100644
index 0000000..144ae06
--- /dev/null
+++ b/test/type.js
@@ -0,0 +1,44 @@
+var test = require('tap').test;
+var deepFreeze = require('../');
+
+/**
+ * Test freeze method (freeze, seal, or preventExtensions).
+ */
+
+test('freeze', function (t) {
+  "use strict";
+
+  t.plan(4);
+
+  var a = {
+    // a function
+      b: function() {},
+  };
+
+  deepFreeze(a, 'freeze');
+  t.assert(Object.isFrozen(a));
+  t.assert(Object.isFrozen(a.b));
+  try {
+    a.x = 5;
+  } catch (e) {
+    t.ok('error thrown as expected');
+  }
+  t.equal(a.x, undefined);
+});
+
+test('bad type', function (t) {
+  "use strict";
+
+  t.plan(1);
+
+  var a = {
+    // a function
+      b: function() {},
+  };
+
+  try {
+    deepFreeze(a, 'whoops');
+  } catch (e) {
+    t.ok('error thrown as expected');
+  }
+});
\ No newline at end of file