This volume constitutes the proceedings of 23rd International Conference on Software Engineering and Formal Methods, SEFM 2025, held in Toledo, Spain, on November 10–14, 2025.The 13 full papers and 2 short papers included in this book were carefully reviewed and selected from 39 submissions. The proceedings also include 1 invited short paper. They were organized in topical sections as follows: security and resilience; formal specification and verification; software quality; and artificial intelligence and formal methods.