Next-generation distributed applications and systems are increasingly developed using middleware. This dependency poses hard R&D challenges, including - tency hiding, masking partial failure, information assurance and security, legacy integration, dynamic service partitioning and load balancing, and end-to-end quality of service specification and enforcement. To address these challenges, researchers and practitioners must discover and validate techniques, patterns, and optimizations for middleware frameworks, multi-level distributed resource management, and adaptive and reffective middleware architectures. Following the success of the past IFIP/ACM Middleware conferences (Lake District/UK, Palisades/USA, and Heidelberg/Germany) and building upon the success of past USENIX COOTS conferences, the Middleware 2003 conference is the premier international event for middleware research and technology. The scope of the conference is the design, implementation, deployment, and eval- tion of distributed system platforms, architectures, and applications for future computing and communication environments. This year, we had a record of 158 submissions, among which the top 25 - pers were selected for inclusion in the technical program of the conference. All papers were evaluated by at least three reviewers with respect to their origin- ity, technical merit, presentation quality, and relevance to the conference themes. The selected papers present the latest results and breakthroughs on middleware research in areas including peer-to-peer computing, publish-subscriber archit- tures, component- and Web-based middleware, mobile systems, and adaptive computing.