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. Grid and Pervasive Computing (GPC) is an annual international conference devoted to the promotion and advancement of all aspects of grid and pervasive computing. The objective of this conference is to provide a forum for researchers and engineers to present their latest research in the ?elds of grid and pervasive computing. Previous editions of the Grid and Pervasive Computing conference were held in: Kunming (China) May 25-28, 2008, Paris (France) May 2-4, 2007, and Taichung (Taiwan) May 3-5, 2006. The fourth edition took place in Geneva, Switzerland during May 4-8, 2009. It was organized by members of the University of Applied Sciences Western Switzerland (Haute Ecole de Paysage, d¿Ing¿ enierie et d¿Architecture - hepia), in collaboration with colleagues from various places around the world. The conference spanned a full week, including a three-day technical program where the papers contained in these proceedings were presented. The conf- ence was followed by two tutorial days where attendants had the opportunity to discuss a variety of topics related to the ?elds covered at the conference, at both introductory and advanced levels. The technical program also included an industrial session, with contributions illustrating challenges faced and so- tions devised by industry. Furthermore, the conference o?ered an opportunity for vendors and researchers to present their products and projects at an ex- bition (Grid Village) where solutions supporting the development of grid and pervasive computing were displayed.