This book constitutes the thoroughly refereed post-proceedings of the 6th International Conference on Theory and Applications of Satisfiability Testing, SAT 2003, held in Santa Margherita Ligure, Italy, in May 2003. The 33 revised full papers presented together with 5 articles reporting results of the related SAT competition and QBF evaluation were carefully selected during two rounds of reviewing and improvement from 67 submissions. The whole spectrum of research in propositional and quantified Boolean formula satisfiability testing is covered including proof systems, search techniques, probabilistic analysis of algorithms and their properties, problem encodings, industrial applications, specific tools, case studies, and empirical results.