This book constitutes the refereed proceedings of the 6th European Meeting of the Parallel Virtual Machine and Message Passing Interface Users' Group, PVM/MPI '99, held in Barcelona, Spain in September 1999. The 67 revised papers presented were carefully reviewed and selected from a large number of submissions. All current issues of PVM and MPI are addressed. The papers are organized in topical sections on evaluation and performance, extensions and improvements, implementation issues, tools, algorithms, applications in science and engineering, networking, and heterogeneous distributed systems.