This book constitutes the refereed proceedings of the 15th IFIP WG 6.1 International Conference on Formal Methods for Open Object-Based Distributed Systems, FMOODS 2013, and the 33rd IFIP WG 6.1 International Conference on Formal Techniques for Networked and Distributed Systems, FORTE 2013, held in Florence, Italy, in June 2013, as part of the 8th International Federated Conference on Distributed Computing Techniques, DisCoTec 2013. The 20 revised full papers presented were carefully reviewed and selected from 39 submissions. The papers present a wide range of topics combining theory and practice. They cover distributed computing models and formal specification, testing, and verification methods as well as application domains such as application-level distributed systems, telecommunication services, Internet, embedded and real-time systems, and networking and communication security and reliability.