This paper describes our experience implementing CES, a distributed Collaborative Editing System written in Argus, a language that includes facilities for managing long-!ived distributed data. Argus provides atomic actions, which simplify the handling of concurrency and faihres, and mechanisms for implementing atomic data ~5'pes, which ensure serializability and recoverability of actions that use them. This paper focuses on the support for atomicity in Argus, espedatly the support for building new atomic types. Overall the mechanisms in Argus made it relatively easy to build CES; however, we encountered interesting problems in several areas° For example, much of the processing of an atomic action in Argus is handled automatically by the run4ime system; several examples are presented that illustrate areas where more explicit control in the implementations of atomic types would be useful.