diff --git a/mqtt_codec/packet.py b/mqtt_codec/packet.py
index <HASH>..<HASH> 100644
--- a/mqtt_codec/packet.py
+++ b/mqtt_codec/packet.py
@@ -3,6 +3,10 @@
 `mqtt_codec.packet` Package
 ============================
 
+A collection of classes used to represent MQTT control packets as
+described in the specification.  The classes are, in general,
+immutable; once a class has been instantiated its properties cannot be
+changed.
 
 """
Updated mqtt_codec.packet docstrings.