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. This year EXPRESS is co-located with CONCUR '08, held in Toronto. In response to the call for papers, we received one short paper and 12 full papers. The program committee selected 8 of the full papers for presentation at the workshop. In addition, the workshop contains two invited presentations, by Michele Bugliesi (invited jointly with the SECCO workshop) and Gianluigi Zavattaro. The selected full papers and abstracts for the invited talks appear in these preliminary proceedings. We would like to thank the authors of the submitted papers, the invited speakers, the members of the program committee, and their subreferees for their contribution to both the meeting and this volume. Also we thank the CONCUR organising committee for hosting EXPRESS '08, and Richard Trefler for the local organization of the workshops and arranging the printing of these preliminary proceedings, which were compiled by Espen Højsgaard. The final proceedings will become available electronically at Elsevier's web site http://www.elsevier.com/locate/entcs.