This article argues that psycholinguists need to think in a different way to understand processing in dialogue. According to this view, interlocutors do not use language to encode and decode messages, but rather as a means by which they can align their mental states, so that they come to have the same ideas about the topic under discussion. It would in principle be possible to decompose this task into discrete acts of comprehension and production, but in practice real dialogue involves constant overlaying of production and comprehension. It is much better to understand dialogue as a joint activity, like ballroom dancing or using a two-handed saw, and to assume that alignment follows from this inherently interactive process. On the assumption that the goal of dialogue is alignment, this article discusses ways in which interlocutors come to achieve this state. First, it considers alignment via beliefs about one's interlocutor, and then discusses alignment via imitation. The article also looks at alignment via agreements between interlocutors, alignment via feedback, and alignment via physical co-presence.