The Fourth European Symposium on Organic Micropollutants in the Aquatic Environment was held in Vienna (Austria) from 22 to 24 October 1985. The Symposium was organized wi thin the framework of the Concerted Action COST 641* which is included in the Third R&D Programme on the Environment of the Commission of the European Communities. The aim of the Symposium was to review recent scientific and technical progress in the area of organic micropollutants in the aquatic environment and to present relevant research papers related to analytical methodologies, transformation reactions and transport of organic micropollutants in water, and water treatment processes. A special session was devoted to theoretical aspects and future acti vi ties. Furthermore, special poster sessions were organized where original contributions were presented. This book presents the Proceedings of the Symposium including all review papers, presentations of research papers and extended versions of all posters. We believe that these Proceedings provide a good overview of the activities in this field in Europe. We are confident that it will constitute a valuable contribution to the understanding and solution of the problems posed by organic micropollutants in the aquatic environment. The Commission of the European Communi ties whishes to express its grati tude to the co-organizers of the Symposium, Bundesministerium fUr Gesundheit und Umweltschutz, Wien, and Der Osterreichische Wasserwirtschaftsverband.