We present a formal model of opinion diffusion and formation which combines notions from social network analysis together with concepts and techniques from judgment aggregation and merging. The model allows us to study the propagation of individual opinions, represented in the form of yes/no answers to a set of multiple binary issues, in a multiagent system linked by an influence network. The process is iterative with discrete time. We are interested in characterizing properties of the network structure which guarantee convergence of the iterative process for every initial configuration of the agents' opinions, and in developing tractable algorithms for computing the set of opinions at convergence.