This volume contains the Proceedings of the Sixth French-German Conference on Optimization, which took place in June 1991 at Lambrecht (PfaIz). About one hundred scientists, mainly from France and Germany, but also from other european countries, met at the Palatinate Conference Center in the heart of the beautiful palatinate national park to review and discuss recent developments in the field of optimization. More than sixty lectures were delivered, covering a large part of the theoretical and practical aspects of optimization. They all contributed to a stimulating scientific exchange during...