Organized by the Ecole des Mines de Nantes in partnership with the LINA and the INRIA, the 9th international CPAIOR conference will be held in Nantes, in France, from May 28 to June 1, 2012.The CPAIOR 2012 conference aims at gathering researchers from constraint programming (CP), artificial intelligence (AI) and operations research (OR) to present new techniques or applications in combinatorial optimization and to provide an opportunity for researchers in one area to learn about techniques in the other ones.