This book constitutes the refereed proceedings of the 6th IFIP WG 6.1 International Conference on Formal Methods for Open Object-Based Distributed Systems, FMOODS 2003, held in Paris, France in November 2003.The 18 revised full papers presented together with an invited paper were carefully reviewed and selected from 78 submissions. The papers are organized in topical sections on models, logic and verification, calculi, Java and .NET, UML, and composition and verification.