This survey introduces existing approaches to Agent Communication Languages (ACLs) and particularly Conversation Policies (CPs) which can be viewed as general constraints on the sequence of semantically coherent messages leading to a goal. Then limitations of these CPs are discussed in detail, particularly limitations on flexibility and specification. Finally, ACLs are viewed from the dialectic point of view, and some approaches are introduced in this context: some focusing on commitment-based protocols and others on dialogue-game-based protocols.