In the past ten years or so, software architecture has emerged as a central notion in the development of complex software systems. Software architecture is now accepted in the software engineering research and development community as a manageable and meaningful abstraction of the system under development and is applied throughout the software development life cycle, from requirements analysis and validation, to design and down to code and execution level. This book presents the tutorial lectures given by leading authorities at the Third International School on Formal Methods for the Design of Computer, Communication and Software Systems, SFM 2003, held in Bertinoro, Italy, in September 2003. The book is ideally suited for advanced courses on software architecture as well as for ongoing education of software engineers using formal methods in their day-to-day professional work.