diff --git a/docs/source/decisions/0005-comma-separated-values.rst b/docs/source/decisions/0005-comma-separated-values.rst
new file mode 100644
index 000000000..2a5627fa9
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+++ b/docs/source/decisions/0005-comma-separated-values.rst
@@ -0,0 +1,70 @@
+Statement
+=========
+
+Continue to allow Comma Separated Values (CSV) and JavaScript Object Notation (JSON) as formats going forward. CWMS Data API (CDA) will officially
+support JSON and CSV. Additional formats may be introduced via versioned
+changes or explicit content negotiation if a documented use case arises.
+
+Purpose / Need
+==============
+
+CSV
+---
+
+CSV, without a viewing software, is also highly viewable by humans compared to
+JSON.
+
+CSV isolates tabular datasets and minimizes structural overhead, making it
+easier to inspect in spreadsheet-oriented workflows. It is easily imported
+into various end-user client software (MS Excel/Sheets), and does not require
+extra code on the client in order to convert from one format to another when
+JSON is the only option.
+
+if end-users wanted to easily manipulate data without first needing to parse it in JSON they would
+be able to do so with CSV.
+
+Example: Sharing a link to a specific dataset. This can be handled via a direct
+CDA link that when clicked, downloads the CSV file directly.
+
+*Relies on*: ``Content-Type: text/csv`` being set by default.
+
+JSON
+----
+
+JSON is the default response format. Some legacy endpoints currently return XML
+due to upstream constraints; these are considered transitional and should be
+normalized where feasible.
+
+It works well with downstream programming needs and offers additional metadata
+beyond what CSV provides.
+
+Expectations
+============
+
+1. Query parameter (``?format=``) overrides ``Accept`` header to support browser
+   downloading via URI control.
+
+   - If neither is present, default to JSON.
+
+2. CSV must only include the headers and data fields. No additional metadata, text, or comments at
+   the top.
+
+   - UTF-8 encoded
+   - Empty values **must** return empty fields, **not** ``null``.
+     Example: ``date,4.0,,`` **not** ``date,4.0,null,null``
+     This ensures smaller file sizes and compatibility with common CSV parsers.
+
+3. If data response types must change, such as headers or key-value pairs in a
+   response, the version **must** be updated to reflect this in the
+   ``Accept`` header to match the practices already in place for versioning. See :doc:`Versioning policy <./0004-data-versioning.rst>` for details.
+
+
+4. Error handling requirements:
+    
+    Proper errors must be returned when a format fails to parse (e.g. invalid JSON or a CSV file that does not contain any data or fails to render).    
+
+   - ``400 Bad Request`` MUST be returned for malformed or invalid client input
+   - ``415 Unsupported Media Type`` MUST be returned when the requested format is
+     recognized but not supported for the endpoint
+   - ``406 Not Acceptable`` MUST be returned when the requested media type will
+     never be supported by the endpoint
\ No newline at end of file
diff --git a/docs/source/decisions/index.rst b/docs/source/decisions/index.rst
index 80a24751a..8e095bd27 100644
--- a/docs/source/decisions/index.rst
+++ b/docs/source/decisions/index.rst
@@ -21,3 +21,4 @@ Some decisions may also be a proposal and marked appropriately.
     Data Versioning <./0002-data-versioning.rst> (rejected, remains for historical context.)
     Catalogs and Search <./0003-searchability-and-catalogs.rst>
     Versioning <./0004-versioning.rst>
+    Comma Separated Values <./0005-comma-separated-values.rst>