This book constitutes the refereed proceedings of the 25th International Symposium on Formal Methods, FM 2023, which took place in Lübeck, Germany, in March 2023. The 26 full paper, 2 short papers included in this book were carefully reviewed and selected rom 95 submissions. They have been organized in topical sections as follows: SAT/SMT; Verification; Quantitative Verification; Concurrency and Memory Models; Formal Methods in AI; Safety and Reliability. The proceedings also contain 3 keynote talks and 7 papers from the industry day.