The ability to reason about action and change has long been considered a necessary component for any intelligent system. Many proposals have been offered in the past to deal with this problem. In this paper, we offer a new approach to belief change associated with performing actions that addresses some of the shortcomings of these approaches. In particular, our approach is based on a well-developed theory of action in the situation calculus extended to deal with belief. Moreover, our account handles nested belief, belief introspection, mistaken belief, and handles belief revision and belief update together with iterated belief change.