This Book Is Devoted To The 6th International Conference On Theory And Applications Of Satisability Testing (sat 2003) Held In Santa Margherita Ligure (genoa,italy), During May 5-8,2003. Sat 2003 Followed The Workshops On S- Is?ability Held In Siena (1996), Paderborn (1998), And Renesse (2000), And The Workshop On Theory And Applications Of Satis?ability Testing Held In Boston (2001) And In Cincinnati (2002). As In The Last Edition, The Sat Event Hosted A Sat Solvers Competition, And, Starting From The 2003 Edition, Also A Quanti?ed Boolean Formulas (qbfs) Solvers Comparative Evaluation. There Were 67 Submissions Of High Quality, Authored By Researchers From All Over The World. All The Submissions Were Thoroughly Evaluated, And As A Result 42 Were Selected For Oral Presentations, And 16 For A Poster Presentation. The Presentations Covered The Whole Spectrum Of Research In Propositional And Qbf Satis?ability Testing, Including Proof Systems, Search Techniques, Probabilistic Analysis Of Algorithms And Their Properties, Problem Encodings, Industrial App- Cations, Specific Tools, Case Studies And Empirical Results. Further, The Program Was Enriched By Three Invited Talks, Given By Riccardo Zecchina (on Survey Propagation: From Analytic Results On Random K-sat To A Message-passing Algorithm For Satis?ability), Toby Walsh (on Challenges In Sat (and Qbf)) And Wolfgang Kunz (on Atpg Versus Sat: Comparing Two Paradigms For Boolean Reasoning). Sat 2003 Thus Provided A Unique Forum For The Presentation And Discussion Of Research Related To The Theory And Applications Of Pro- Sitional And Qbf Satis?ability Testing.