This paper considers the efficiency and convergence properties of dynamic processes of social and economic interactions. The key general feature of the economy is that agents can implement any move from one state to another as long as a pre-specified subset of agents approve of it. We show that inefficiencies may occur even in the long run. When agents are sufficiently patient, we show very generally that the initial state from which the process starts plays no role in the long run properties of equilibria. Also, when there exists an efficient state that is externality free (in the sense that a move away from that state does not hurt the agents whose consent is not required for the move), then the system must converge to this efficient state in the long run. Conversely, long run efficiency can only be attained in a robust way if there exists an efficient externality-free state.