This book constitutes the refereed proceedings of the 11th International Conference on Tools and Algorithms for the Construction and Analysis of Systems, TACAS 2005, held in Edinburgh, UK in April 2005 as part of ETAPS.The 33 revised full research papers and 8 revised tool demonstration papers presented together with an invited paper were carefully reviewed and selected from a total of 161 submissions. The papers are organized in topical sections on regular model-checking, infinite state machines, abstract interpretation, automata and logics, probabilistic systems and probabilistic model checking, satisfiability, testing, abstraction and reduction, specification and program synthesis, and model-checking.