This book constitutes the refereed proceedings of the 20th International Conference on Integrated Formal Methods, iFM 2025, which took place in Paris, France, during November 19–21, 2025.

The 23 full papers presented together with 1 invited paper in this volume were carefully reviewed and selected from 69 submissions. The conference focuses on all aspects of formal methods, including deductive verification, model checking, reachability analysis, model-based testing, synthesis, timing and stochastic modelling, cyber-physical systems, autonomous systems, security and blockchain.