This book constitutes the refereed proceedings of the 12th International SDL Forum, SDL 2005, held in Grimstad, Norway.

The 16 revised full and 8 short papers presented were carefully reviewed and selected for inclusion in the book. The papers are organized in topical sections on language issues, engineering issues, message sequence charts, applications and tools, model driven architecture, test and validation, and code generation. Thus all aspects of system design using system design languages are addressed.