diff --git a/spec.md b/spec.md
index 0e75baa15..20c2ea78f 100644
--- a/spec.md
+++ b/spec.md
@@ -98,6 +98,30 @@ types of information: the [Data](#data) representing the Occurrence and
 [Context](#context) metadata providing contextual information about the
 Occurrence.
 
+#### Producer
+
+The "producer" is a specific instance, process or device that creates the data
+structure describing the CloudEvent.
+
+#### Source
+
+The "source" is the context in which the occurrence happened. In a distributed
+system it might consist of multiple [Producers](#producer). If a source is not
+aware of CloudEvents, an external producer creates the CloudEvent on behalf of
+the source.
+
+#### Consumer
+
+A "consumer" receives the event and acts upon it. It uses the context and data
+to execute some logic, which might lead to the occurrence of new events.
+
+#### Intermediary
+
+An "intermediary" receives a message containing an event for the purpose of
+forwarding it to the next receiver, which might be another intermediary or a
+[Consumer](#consumer). A typical task for an intermediary is to route the event
+to receivers based on the information in the [Context](#context).
+
 #### Context
 
 Context metadata will be encapsulated in the