This book constitutes the refereed proceedings of the 9th International Conference on Integration of AI and OR Techniques in Constraint Programming for Combinatorial Optimization Problems, CPAIOR 2012, held in Nantes, France, in May/June 2012.The 26 revised full papers presented were carefully reviewed andselected from 64 submissions. The papers are focused on both theoretical and practical, application-oriented issues in combinatorial optimization and feature current research with a special focus on inference and relaxation methods, integration methods, modeling methods, innovative applications of CP/AI/OR techniques, and implementation of CP/AI/OR techniques and optimization systems.