One of the main research objectives of computer science is the development of formal methods for the design and implementation of concurrent programming languages. A most prominent feature of this research area is the proliferation of programming concepts arising from imperative programming, logic programming, functional programming, object-oriented programming, constraint programming, and the various formalizations thereof.

The Human Capital and Mobility project EXPRESS has aimed at a general understanding of the interconnections and relations between formal systems for concurrency, ranging from programming languages to axiom systems and rewrite systems. More specifically, we have compared programming concepts and formalisms on the basis of their relative expressive power. The results obtained in our project are steps towards classifying the variety of concurrent programming languages, and may provide a formal basis for their design and implementation.

The partners of EXPRESS have been the CWI (Amsterdam), the University of Utrecht, the University of Florence, the University of Aalborg, the University of Nijmegen, the Swedish Institute of Computer Science, the University of Genoa, the University of Rome "La Sapienza", the University of Hildesheim, the University of Amsterdam, INRIA Sophia Antipolis, INRIA Rennes, and the University of Sussex. External partners associated to the project were the State University of New York at Stony Brook, the University at Cornell (USA), the Weizmann Institute (Israel) and the McGill University (Canada). The project ran for four years 1993-1997.

Each year the project partners met at a workshop, disseminating the latest results. The last of these, EXPRESS'97 at Santa Margherita Ligure, Italy, 8-12 September 1997, was also open to the scientific community. Apart from the ordinary EXPRESS presentations we had a general call for papers from outside the project. Among the submissions we selected 13 papers from presentation, which are collected in these proceedings. Additionally we had 7 invited speakers: Ralph Bach, Jean-Jacques Levy, Eugenio Moggi, Ugo Montanari, Amir Pnueli, Vaughan Pratt, and Colin Stirling. Some of the invited speakers also offered a contribution to the proceedings.

We would like to thank the EXPRESS members, the invited speakers, the authors of the submitted papers, and the members of the program committee for their contribution to both the meeting and this volume. We also would like to thank Elisabetta Ferrando for help with the local organization and Michael Mislove for editorial help with the proceedings.

Catuscia Palamidessi, University of Genova, Italy
Joachim Parrow, Royal Institute of Technology, Stockholm, Sweden

EXPRESS'97 Programme Committee
Luca Aceto (Aalborg) Eike Best (Oldenburg)
Frank de Boer (Utrecht) Ilaria Castellani (Sophia Antipolis)
Philippe Darondeau (Rennes) Rocco De Nicola (Florence)
Ursula Goltz (Hildesheim) Jan Willem Klop (CWI)
Catuscia Palamidessi (co-chair) (Genoa) Joachim Parrow (co-chair) (Stockholm)
Frits Vaandrager (Nijmegen)