The Fifth International Conference on Operations Research (CIRO'10) will be held in Marrakech from 24 to 27 May 2010. The CIRO manifestation is an event jointly organized by the Team of Mathematics of Decision Support, Faculty of Science Semlalia, Cadi Ayyad University, Marrakech and the Group of Optimization Department of Computer Science, University of Sherbrooke Canada, in partnership with the National Higher School of Computer Science and Systems Analysis (ENSIAS) and the Moroccan Society of Operations Research (SOMARO). This conference aims to bring together researchers and operational scientists from various countries to take stock of the latest developments in the field both in theory and applications.