This book constitutes the refereed proceedings of the 4th IFIP WG 6.1 International Conference on Distributed Applications and Interoperable Systems, DAIS 2003, held in Paris, France, in November 2003.The 21 revised full papers and 6 revised short papers presented were carefully reviewed and selected from a total of 88 submissions. The papers are organized in topical sections on adaptation and separation of concerns; deployment; security and transactions; replication; networking and routing; discovery, context-awareness, and ontologies; and asynchronous messaging.