This book constitutes the thoroughly refereed post-proceedings of the 8th International Conference on Principles of Distributed Systems, OPODIS 2004, held at Grenoble, France, in December 2004. The 30 revised full papers presented together with abstracts of 2 invited talks were carefully reviewed and selected from 102 submissions. The papers are organized in topical sections on design of distributed systems, ad-hoc networks and mobile agents, grid and networks, security, distributed algorithms, self-stabilization, sensor networks, and task/resource allocation.