Introduction: What’s happening in the brains of two people having a conversation? One reasonable guess is that in the fMRI scanner we’d see most of their brains light up. Another is that their EEG will be a total mess, reflecting dozens of interacting neuronal systems. Conversation recruits all of the basic language systems reviewed in this book. It also heavily taxes cognitive systems more likely to be found in handbooks of memory, attention and control, or social cognition (Brownell & Friedman, 2001). With most conversations going beyond the single utterance, for instance, they place a heavy load on episodic memory, as well as on the systems that allow us to reallocate cognitive resources to meet the demands of a dynamically changing situation. Furthermore, conversation is a deeply social and collaborative enterprise (Clark, 1996; this volume), in which interlocutors have to keep track of each others state of mind and coordinate on such things as taking turns, establishing common ground, and the goals of the conversation.