A weakest precondition semantics for communicating processes is presented, based on a centralized, one-level approach. Semantic equations are given for the CSP constructs and their continuity is proved. The equivalence of two weakest precondition definitions, one with certain order preferences, and another one, preference-free, is shown. The representation of various operational concepts, including delay, is discussed. Several examples of applying the rules are given. © 1984.