Of interest to those involved in the design of complex distributed systems, this volume presents papers concerning the Formal Description Technique Estelle. It includes a general survey and technical papers on: the semantics of Estelle, selected application examples, extensions and relationships with Petri nets, verification methods with software prototypes and an implementation support package for edition, simulation and code generation. The SEDOS (Software Environment for the Design of Open Distributed Systems) project was supported by the Commission of the European Communities under the ESPRIT Programme. It was divided into two main tasks, related respectively to the two ISO formal description techniques Estelle and LOTOS, which became international standards in September 1988. Estelle has been developed in close collaboration with the TC97-SC21-WG1 group on Formal Description Techniques of ISO.