This book includes extended and revised versions of selected papers from the 11th and 12th editions of the International Conference on Operations Research and Enterprise Systems (ICORES 2022 and ICORES 2023). ICORES 2022 was held as a virtual event in February 2022, and ICORES 2023 was held in Lisbon, Portugal, in February 2023. The 5 full papers included in this book were carefully reviewed and selected from the 55 submissions for ICORES 2022, and 8 full papers were reviewed and selected from the 55 submissions for ICORES 2023. The papers are focused on operations research and enterprise systems.