This book constitutes the refereed proceedings of the 12th IFIP WG 6.1 International Conference on Formal Methods for Open Object-Based Distributed Systems, FMOODS 2010, and the 30th IFIP WG 6.1 Formal Techniques for Networked and Distributed Systems, FORTE 2010, held in Amsterdam, The Netherlands, in June 2010. The 13 revised full papers presented together with 6 short papers and the abstract of one invited talk were carefully reviewed and selected from 38 submissions. The papers are organized in topical sections on formal UML modeling; components and architecture; timed process algebra; timed and hybrid automata; program logics and analysis; and reasoning about distributed systems.