diff --git a/api/identity/lookup.yaml b/api/identity/lookup.yaml
index 18e5e77d..4d5ab5b7 100644
--- a/api/identity/lookup.yaml
+++ b/api/identity/lookup.yaml
@@ -82,4 +82,57 @@ paths:
                 description: The unix timestamp at which the association was verified.
               signatures:
                 type: object
-                description: The signatures of the verifying identity service which show that the association should be trusted, if you trust the verifying identity service.
+                description: The signatures of the verifying identity services which show that the association should be trusted, if you trust the verifying identity services.
+  "/bulk_lookup":
+    post:
+      summary: Lookup Matrix user IDs for a list of 3pid.
+      description: Lookup Matrix user IDs for a list of 3pid.
+      parameters:
+        - in: body
+          name: body
+          schema:
+            type: object
+            example: {
+              "threepids":
+              [
+                ["email","user@example.org"],
+                ["msisdn", "123456789"],
+                ["email","user2@example.org"]
+              ]
+            }
+            properties:
+              threepids:
+                type: array
+                items:
+                  type: array
+                  title: 3PID mappings
+                  items:
+                    type: string
+                    title: 3PID medium or address
+                description: an array of array containing the `3PID Medium type`_ in first position and the 3PID Address in second position.
+            required:
+              - "threepids"
+      responses:
+        200:
+          description: A list of known 3PID mappings for the supplied 3PIDs.
+          examples:
+            application/json: {
+              "threepids": [
+                ["email","user@example.org", "@bla:example.org"],
+                ["msisdn", "123456789", "@blah2:example.com"]
+              ]
+            }
+          schema:
+            type: object
+            properties:
+              threepids:
+                type: array
+                items:
+                  type: array
+                  title: 3PID mappings
+                  items:
+                    type: string
+                    title: 3PID medium or address or the Matrix ID
+                description: an array of array containing the `3PID Medium type`_ in first position, the 3PID Address in second position and Matrix ID is in third position.
+            required:
+              - "threepids"
diff --git a/specification/identity_service_api.rst b/specification/identity_service_api.rst
index fa03e162..85b9789f 100644
--- a/specification/identity_service_api.rst
+++ b/specification/identity_service_api.rst
@@ -291,3 +291,4 @@ It will look up ``token`` which was stored in a call to ``store-invite``, and fe
  }
 
 .. _`Unpadded Base64`:  ../appendices.html#unpadded-base64
+.. _`3PID Types`:  ../appendices.html#pid-medium-types