This volume contains a selection of papers referring to lectures presented at the symposium "Operations Research 2004" (OR 2004) held at Tilburg University, September 1-3, 2004. This international conference took place under the auspices of the German Operations Research Society (GOR) and the Dutch Operations Research Society (NGB). The symposium had about 500 participants from countries all over the world. It attracted academics and practitioners working in various fields of Operations Research and provided them with the most recent advances in Operations Research and related areas in Economics, Mathematics, and Computer Science. The program consisted of 4 plenary and 19 semi-plenary talks and more than 300 contributed presentations selected by the program committee to be presented in 20 sections.