This book constitutes the refereed proceedings of the 26th International Conference on Product-Focused Software Process Improvement, PROFES 2025, held in Salerno, Italy, during December 1–3, 2025. The 23 full research papers and 20 short research papers presented in this volume were carefully reviewed and selected from 101 submissions. PROFES 2025 focuses on professional Software Process Improvement (SPI) motivated by product, process, and service quality needs. The technical program was curated by a committee of distinguished experts in software process improvement, software process modeling, and empirical software engineering.!--[endif]--