This book constitutes the refereed proceedings of the 15th European PVM/MPI Users' Group Meeting held in Dublin, Ireland, in September 2008. The 29 revised full papers presented together with abstracts of 7 invited contributions, 1 tutorial paper and 8 poster papers were carefully reviewed and selected from 55 submissions. The papers are organized in topical sections on applications, collective operations, library internals, message passing for multi-core and mutlithreaded architectures, MPI datatypes, MPI I/O, synchronisation issues in point-to-point and one-sided communications, tools, and verification of message passing programs. The volume is rounded off with 4 contributions to the special ParSim session on current trends in numerical simulation