This book constitutes the refereed proceedings of the International Symposium on Fundamentals of Software Engineering, FSEN 2007, held in Tehran, Iran, April 17-19, 2007.The 32 revised papers presented were carefully reviewed and selected from 73 submissions. The topics include Models of programs and systems, Software specification, validation and verification, Software architectures and their description languages, Object and multi-agent systems, Coordination and feature interaction, Integration of formal and informal methods, Integration of different formal methods, Component-based development, Service-oriented development, Model checking and theorem proving, Software and hardware verification and CASE tools and tool integration.