diff --git a/negotiation/contract.negotiation.binding.https.md b/negotiation/contract.negotiation.binding.https.md
index 84349bf5..98bf6a4f 100644
--- a/negotiation/contract.negotiation.binding.https.md
+++ b/negotiation/contract.negotiation.binding.https.md
@@ -231,7 +231,9 @@ Authorization: ...
   "dspace:processId": "urn:uuid:a343fcbf-99fc-4ce8-8e9b-148c97605aab",
   "dspace:agreement": {
     "@type": "odrl:Agreement",
-    "@id": "e8dc8655-44c2-46ef-b701-4cffdc2faa44"
+    "@id": "e8dc8655-44c2-46ef-b701-4cffdc2faa44",
+    "dspace:consumerId": "...",
+    "dspace:providerId": "...",
     }
   }
 }
diff --git a/negotiation/contract.negotiation.protocol.md b/negotiation/contract.negotiation.protocol.md
index 8f56f857..853dbc3a 100644
--- a/negotiation/contract.negotiation.protocol.md
+++ b/negotiation/contract.negotiation.protocol.md
@@ -125,6 +125,11 @@ A `ContractAgreementMessage` must contain an ODRL `Agreement`.
 
 An `Agreement` must contain a `dspace:timestamp` property defined as an XSD DateTime type.  
 
+An `Agreement` must contain a `dspace:consumerId` and `dspace:providerId`. The contents of these
+properties are a dataspace-specific unique identifier of the contract agreement parties. Note that these
+identifiers are not necessarily the same as the identifiers of the participant agents negotiating the
+contract (i.e. the "connectors").
+
 ### 4. ContractAgreementVerificationMessage
 
 
diff --git a/negotiation/message/contract-agreement-message.json b/negotiation/message/contract-agreement-message.json
index 74884688..e4c37681 100644
--- a/negotiation/message/contract-agreement-message.json
+++ b/negotiation/message/contract-agreement-message.json
@@ -9,6 +9,8 @@
       "@value": "2023-01-01T01:00:00Z",
       "@type": "xsd:dateTime"
     },
+    "dspace:consumerId": "...",
+    "dspace:providerId": "...",
     "odrl:permission": {
       ...
     }
diff --git a/negotiation/message/diagram/contract-agreement-message.png b/negotiation/message/diagram/contract-agreement-message.png
index e1f75def..584371fe 100644
Binary files a/negotiation/message/diagram/contract-agreement-message.png and b/negotiation/message/diagram/contract-agreement-message.png differ
diff --git a/negotiation/message/diagram/contract-agreement-message.puml b/negotiation/message/diagram/contract-agreement-message.puml
index 49a707f4..4531f193 100644
--- a/negotiation/message/diagram/contract-agreement-message.puml
+++ b/negotiation/message/diagram/contract-agreement-message.puml
@@ -19,6 +19,8 @@ class odrl:Agreement {
     @id: String
     odrl:target : xsd:anyURI
     dspace:timestamp : xsd:dateTime
+    dspace:consumerId : String
+    dspace:providerId : String
 }
 
 "dspace:ContractAgreementMessage" "1" *-- "1" "odrl:Agreement" : "odrl:agreement"
diff --git a/negotiation/message/example/contract.agreement.message.http.transfer.json b/negotiation/message/example/contract.agreement.message.http.transfer.json
index 6a97919a..3c67f216 100644
--- a/negotiation/message/example/contract.agreement.message.http.transfer.json
+++ b/negotiation/message/example/contract.agreement.message.http.transfer.json
@@ -3,6 +3,8 @@
   "@id": "some-id",
   "@type": ["dspace:ContractAgreementMessage"],
   "dspace:processId": "urn:uuid:a343fcbf-99fc-4ce8-8e9b-148c97605aab",
+  "dspace:consumerId": "...",
+  "dspace:providerId": "...",
   "dspace:agreement": {
     "@type": "odrl:Agreement",
     "@id": "some-other-id",
diff --git a/negotiation/message/schema/contract-agreement-message-schema.json b/negotiation/message/schema/contract-agreement-message-schema.json
index cbb6664c..7dab4f35 100644
--- a/negotiation/message/schema/contract-agreement-message-schema.json
+++ b/negotiation/message/schema/contract-agreement-message-schema.json
@@ -54,10 +54,18 @@
 									"required": true
 								}
 							}
+						},
+						"dspace:consumerId": {
+							"type": "string",
+							"required": true
+						},
+						"dspace:providerId": {
+							"type": "string",
+							"required": true
 						}
 					}
 				}
 			}
 		}
 	}
-}
+}
\ No newline at end of file