Introduction and Overview. SEDOS Software Environment for the Design of Open Distributed Systems (M. Diaz, C.A. Vissers, J.-P. Ansart). LOTOS Backgrounds (C.A. Vissers). Introduction to the ISO Specification Language LOTOS (T. Bolognesi, E. Brinksma). Specification. LOTOS Language Development and Promotion in the SEDOS Project (J. Quemada). A Constraint Oriented Specification of Al's Node (J. Quemada, A. Azcorra). Formal Description of the OSI Session Layer: Introduction (I. Ajubi, G. Scollo, M. van Sinderen). Formal Description of the OSI Session Layer: Transport Service (G. Scollo). Formal Description of the OSI Session Layer: Session Service (M. van Sinderen). Formal Description of the OSI Session Layer: Session Protocol (I. Ajubi). The OSI Transaction Processing Service: A Formal Framework (M. van Sinderen). Connectionless Data Link Service (J. Quemada, F. Fournon). Verification. LOTOS Verification Aspects: Report of the SEDOS C2 Task (E. Brinksma). A Theory for the Derivation of Tests (E. Brinksma). Towards Algebraic Semantics of the ISO-Specification Language LOTOS (H. Ehrig et al.). A Verification Oriented Specification in LOTOS of the Transport Protocol (E. Najm). PERLON Persistency Checker for Data Type Definitions (P. Bohm, J. de Meer, P. Schoo). Equivalence Verification: Theory, Algorithms, and a Tool (T. Bolognesi, M. Caneve). TILT: From LOTOS to Labelled Transition Systems (H. Garavel, E. Najm). Tools. Introduction to LOTOS Tools (A.K. Marshall). The Design of a Simulator Tool (P.H.J. van Eijk). HIPPO: A LOTOS Simulator (J. Tretmans). Functionality of an ADT Interpreter (R.B. Alderden). The Implementation of a Specification Language for OSI Systems (J.A. Ma#as, T. de Miguel, H. van Thienen). On the Correctness of Implementations of LOTOS Behaviour Specifications (H. van Thienen, J.A. Ma#as, T. de Miguel). Dining Philosophers: A Constraint Oriented Specification (J.A. Ma#as).