In recent years in computer science and multi-agent systems there has been a lot of interest in exploring ways to aggregate the logical beliefs and opinions of a set of individual agents into a single, coherent group belief which reflects the opinion of the group as a whole. However there is little work that analyses the evolution of these group beliefs over time. This is surprising, given that the question of how an individual agent changes its beliefs has been well studied in the area of Belief Revision. A change in the group belief may be brought about in several different ways. An individual agent may change its own belief in response to either its own private external observation or to information communicated to it by other agents in the group. In the latter case the receiving agent may choose whether or not to accept the information based on the perceived trust level of the other agent. Either way, when fed into the aggregation operator, the agent’s new belief may cause a change in the group belief. In this setting several interesting questions arise, such as: what does agent A need to communicate, and to whom, in order to achieve a certain desired aggregation outcome? Also if all agents make the same external observation and then aggregate, what is the relationship between the new group beliefs and the old? This project will establish qualitative properties of the dynamics of group beliefs. The proposed theory will yield new insights on belief diffusion in social networks.