This book constitutes the refereed proceedings of the 25th International Conference on Mathematical Optimization Theory and Operations Research, MOTOR 2026, held in Irkutsk, Russia, during July 6–11, 2026.The 26 full papers and 2 short papers presented in this volume were carefully reviewed and selected from 56 submissions. They are grouped into the following topics: Mathematical Programming; Discrete and Combinatorial Optimization; Stochastic Optimization; Scheduling; Applications in Machine Learning and Mathematical Economics; Optimal Control; Optimal Control.