This paper is concerned with argumentation-based dialogues between agents. Much work in this area has been based upon an influential taxonomy of dialogue types developed by Walton and Krabbe. This paper re-examines the Walton and Krabbe framework, concentrating on the preconditions for different types of dialogue and analyzing these in a systematic way. Doing so uncovers some inconsistencies in previous interpretations of the preconditions and, in resolving these inconsistencies, identifies a number of new kinds of dialogue. We discuss some of the more interesting of these new kinds of dialogue and give protocols for them. Categories and Subject Descriptors I.2.11 [Artificial Intelligence]: Distributed Artificial Intelligence— Coherence and co-ordination; multiagent systems. General Terms Languages, theory. Keywords Agent communication, dialogue games, argumentation.