This volume contains the proceedings of the 200 I International Conference on Operations Research (OR 2(01) held at the Gerhard-Mercator-University Duisburg, September 3-5,2001. OR 200 1 was organized under the auspices of the German Society of Operations Research, Gesellschaft für Operations Research (GOR e. V.). The conference and the annual general meeting were attended by 360 participants from 20 countries. The presentation of 220 papers was organized in 15 sections. According to Duisburg as hosting city for this event OR 200 1 emphasized on contributions of OR in the areas of energy, transport and traftk. The program consisted of2 plenary lectures (Reinhard Selten and Jörg Hennerkes) and 15 invited semiplenary lectures. 97 papers were submitted for publication. Following the advice of the section chairs the program committee decided to accept 59 papers for this volume. The selected manuscripts will be published also in electronic form on the W orld Wide Web at http://www.uni-duisburg.de/or200 1. We want to thank all referees and authors for delivering their final manuscript in due time. We are also grateful to the other members of the local organizing committee and especially to Stefan Krebs, Corinna Schu and David Betge for the perfect conference management. Roland Düsing, Ralph Gollmer and Steffen Stock supported us in editing the abstracts and the final version of this proceeding volume. Last but not least thanks to all the assistants and student assistants for their operations on OR 2001 in Duisburg.