This book constitutes the refereed proceedings of the 4th European Performance Engineering Workshop, EPEW 2007, held in Berlin, Germany, September 27-28, 2007. The 20 revised full papers presented were carefully reviewed and selected from 53 submissions. The papers are organized in topical sections on Markov Chains, Process Algebra, Wireless Networks, Queueing Theory and Applications of Queueing, Benchmarking and Bounding, Grid and Peer-to-Peer Systems.