This book constitutes the refereed proceedings of the 4th International Conference on Grid and Pervasive Computing, GPC 2009, held in Geneva, Switzerland, in May 2009. The 42 revised full papers presented were carefully reviewed and selected from 112 submissions. The papers are organized in topical sections on grid economy, grid security, grid applications, middleware, scheduling, load balancing, pervasive computing, sensor networks, peer-to peer as well as fault tolerance.