This book constitutes the refereed proceedings of the 45th IFIP WG 6.1 International Conference on Formal Techniques for Distributed Objects, Components, and Systems, FORTE 2025, held in Lille, France, in June 2025, as Part of the 20th International Federated Conference on Distributed Computing Techniques, DisCoTec 2025, during June 16–20, 2025. The 8 full papers and 5 short papers included in this book were carefully reviewed and selected from 25 submissions. They focus on fundamental research on theory, models, tools, and applications for distributed system.