This volume constitutes the refereed proceedings of the Third International Conference on Fundamental Approaches to Software Engineering, FASE 2000, held as part of ETAPS 2000 in Berlin, Germany, in March/April 2000. The 21 revised full papers presented together with three invited contributions and three system descriptions were carefully reviewed and selected from almost 60 submissions. The papers are organized in sections on real-time systems, formal engineering systems, software engineering, object orientation, theory and applications, and case studies.