This volume on formal methods for open object-based distributed systems includes the following important areas: object-oriented design and programming; formal specification of distributed systems; open distributed platforms; types, interfaces and behaviour; and formalisation of object-oriented methods. This volume comprises the proceedings of the International Workshop on Formal Methods for Open Object-based Distributed Systems (FMOODS), sponsored by the International Federation for Information Processing (IFIP) which was held in Florence, Italy, in February 1999.