AbstractThis volume contains the Proceedings of the fifth EXPRESS workshop. The workshop was held in Nice, France, on 7 September 1998, as a satellite event to CONCUR '98.The EXPRESS workshops aim at bringing together researchers interested in the relations between various formal systems, particularly in the field of Concurrency. More specifically, they focus on the comparison between programming concepts (such as concurrent, functional, imperative, logic and object-oriented programming) and between mathematical models of computation (such as process algebras, Petri nets, event structures, modal logics, rewrite systems etc.) on the basis of their relative expressive power.These workshops were originally held as meetings of the HCM project E...