This book constitutes the refereed proceedings of the 27th International Conference on Integer Programming and Combinatorial Optimization, IPCO 2026, held in Padova, Italy, during June 17-19, 2026. The 33 full papers included in this book were carefully reviewed and selected from 113 submissions. The IPCO conference is held under the auspices of the Mathematical OptimizationSociety. It brings together researchers and practitioners working on a broad range of topics in integer programming and combinatorial optimization, and has become a premier forum for presenting recent advances in theory, computation, and applications.