This book constitutes the refereed proceedings of the 11th International Workshop on Abstract State Machines, ASM 2004, held in Lutherstadt Wittenberg, Germany, in May 2004. The 12 revised full research papers presented together with 4 invited papers were carefully reviewed and selected for inclusion in the book. The papers reflect state-of-the-art research and development of the abstract state machine method for the design and analysis of complex software and hardware systems. Besides theoretical results and methodological progress, applications in various fields are studied as well.