This proceedings volume contains 6 invited state of the art lectures and 50 contributed papers presented at OR 98 held at the Swiss Federal Institute of Technology (ETH) Zurich, 31 August - 3 September 1998. This 4-annual international conference was jointly organized by the Swiss, German and Austrian OR-societies and co-sponsored by SIGOPT. The conference had 450 particpants from 36 countries around the world. The proceedings of this conference are subdivided according to the eleven sections of the conference, namely - Continuous Mathematical Optimization (8 papers), - Discrete Mathematical...