This book constitutes the refereed proceedings of the 37th IFIP WG 6.1 International Conference on Testing Software and Systems, ICTSS 2025, held in Limassol, Cyprus, during September 17-19, 2025.

The 19 full papers and 4 short papers included in this book were carefully reviewed and selected from 38 submissions. They were organized in topical sections as follows: Foundations and Advanced Testing Techniques; Intelligent and Automated Testing; LLMs, Agents, and AI-Driven Testing; Testing in Complex and Security-Critical Systems. .