This book constitutes the refereed proceedings of the 9th International Conference on Tools and Algorithms for the Construction and Analysis of Systems, TACAS 2003, held in Warsaw, Poland, in April 2003. The 43 revised full papers presented were carefully reviewed and selected from 160 submissions. The papers are organized in topical sections on bounded model checking and SAT-based methods, mu-calculus and temporal logics, verification of parameterized systems, abstractions and counterexamples, real-time and scheduling, security and cryptography, modules and compositional verification, symbolic state spaces and decision diagrams, performance and mobility, state space reductions, constraint solving and decision procedures, and testing and verification.