Bernadette Charron-Bost, Friedemann Mattern, and Gerard Tel Synchronous, Asynchronous, and Causally Ordered Communication. Distributed Computing, Vol. 9 No. 4, pp. 173 - 191, 1996 Summary This article studies characterisic properties of synchronous and asynchronous message communications in distributed systems. Based onthe causality relation between events in computations with asynchronous communications, we characterize computations which are realizable with synchronous communications, which respect causal order, or where messages between two processes are always received in the order sent. It is shown that the corresponding computation classes form a strict hierarchy. Furthermore, an axiomatic definition of distributed computations with synchronous communications is given, and it is shown that several informal characterizations of such computations are equivalent when they are formalized appropriately. As an application, we use our results to show that the distributed termination detection algorithm by Dijkstra et al. is correct under a weaker synchrony assumption than originally stated.