diff --git a/documentation/technical/metadata.md b/documentation/technical/metadata.md
index 1c080243..956ff578 100644
--- a/documentation/technical/metadata.md
+++ b/documentation/technical/metadata.md
@@ -67,6 +67,10 @@ This is for the version of the 360Giving Data Standard being used, so not the ve
 
 Find the details of the current version in the <a href="https://github.com/ThreeSixtyGiving/standard/releases" target="_blank" >Releases changelog</a>. 
 
+**Extensions**
+
+This is a text field that can be used to declare a list of extensions used in the file. Each extension is represented by a short string &ndash; which is a piece of text like a code &ndash; and multiple extensions can be declared by separating them with a semicolon `;` character.
+
 **Title and Description**
 
 These are text fields that can be used to provide information about the name of the file and its contents, and provide further contextual information if appropriate.
diff --git a/documentation/technical/reference.md b/documentation/technical/reference.md
index 39316b7b..ecca6d23 100644
--- a/documentation/technical/reference.md
+++ b/documentation/technical/reference.md
@@ -52,6 +52,7 @@ The [Additional fields](additional-fields) section provides details of all other
 We also provide a version of the <a href="../../_static/360-giving-schema-titles-with-meta-tab-2023.xlsx">360Giving Spreadsheet Template with the Metadata template included</a>. The 'Meta' sheet may be used to publish authoritative metadata about the publisher, the file or dataset. The term we use for this is a 'data package'. The 'Meta' sheet includes sections for:
 
 * The version of the 360Giving Schema used for the file
+* A list of 360Giving extensions used in the file
 * The title and description of the file
 * The dates when the file was first issued and last modified
 * Information about the publisher such as name, logo, website and identifier
diff --git a/schema/360-giving-package-schema.json b/schema/360-giving-package-schema.json
index 930c29d3..55a8b310 100644
--- a/schema/360-giving-package-schema.json
+++ b/schema/360-giving-package-schema.json
@@ -17,6 +17,15 @@
           "type": "string",
           "pattern": "^(\\d+\\.)(\\d+)$"
         },
+	"extensions": {
+	  "title": "Extensions",
+	  "description": "An array of strings which refer to 360Giving Extensions in use by this data file. See the [360Giving Extensions guidance](https://standard.threesixtygiving.org/en/latest/technical/metadata/#field-guidance) for details.",
+	  "type": "array",
+	  "items": {
+	    "type": "string"
+	  },
+	  "uniqueItems": true
+	},
         "title": {
           "title": "Title",
           "description": "The title of the 360Giving data package. Should be a human readable version of information contained in the filename of the data and should be unique ",