diff --git a/Node-Design-Guidelines.md b/Node-Design-Guidelines.md
index 24247e4..7550eff 100644
--- a/Node-Design-Guidelines.md
+++ b/Node-Design-Guidelines.md
@@ -1,5 +1,17 @@
-### Node msg properties
-* [Node msg structure](https://github.com/node-red/node-red/wiki/Node-msg-Conventions)
+### Messages
+* [Message property conventions](https://github.com/node-red/node-red/wiki/Node-msg-Conventions)
+
+### Nodes
+
+There are three types of node.
+
+ - an **Input node** sits at the start of a flow. It is typically triggered by some external event occurring.
+ - a **Function node** sits in the middle of a flow. It performs actions based on the incoming messages and passes on the resulting messages. One sub-type of Function node is a **Query node** that is used to retrieve data from an external API, such as a database query or a web services call.
+ - an **Output node** sits at the end of a flow. It consumes the incoming messages and triggers an action.
+
+---
+Work in progress:
+
 * [[Input node feature definitions]]
 * [[Query node feature definitions]]
 * [[Watch node feature definitions]]