An Interaction Protocol is a kind of Interactive Behavior where Behavior Steps are Interactions that occur between Interaction Roles. The set of Interactions defines the purpose of the Interaction Protocol. A Compound Interaction is an Interaction that is also a Behavior Step, enabling it to reuse an Interaction Protocol. Compound Interaction is complementary to Simple Interaction, which is an Interaction that doesn't have sub-interactions. An Compound Interaction Binding is a Connected Part Binding that specifies how an Interaction Protocol reused by a Compound Interaction ties in with the larger Behavior reusing it. For each Interactive Part involved in a Compound Interaction, there is a Compound Interaction Binding that specifies which Interaction Role it plays in the Interaction Protocol.