We investigate how belief change in cooperative dialogues can be handled within a modal logic of action, belief, and intention. We first review the main approaches of the literature, and point out some of their shortcomings. We then propose a new framework for belief change. Our basic notion is that of a contextual topic: we suppose that we can associate a set of topics with every agent, speech act and formula. This allows us to talk about an agent's competence, belief adoption, and belief preservation. Based on these principles we analyse the agents' belief states after a speech act. We illustrate our theory by a running example.