This book constitutes the refereed proceedings of the 10th European PVM/MPI Users' Group Meeting held in Venice, Italy, in September/October 2003.The 64 revised full papers and 16 revised short papers presented together with abstracts of 8 invited contributions and 7 reviewed special track papers were carefully reviewed and selected from 115 submissions. The papers are organized in topical sections on evaluation and performance analysis; parallel algorithms using message passing; extensions, improvements, and implementations of PVM/MPI; parallel programming tools; applications in science and engineering; grid and heterogeneous computing; and numerical simulation of parallel engineering environments - ParSim 2003.