This volume contains revised versions of papers presented at the NATO Advanced Research Workshop on Data, Expert Knowledge and Decisions held in Hamburg in September 1989. The volume is intended to stimulate cross-disciplinary research concerning - usage of recently developed data analysis procedures in knowledge based systems, - acquisition, representation and management of expert knowledge for specific applications, - building of expert systems in economics and related areas of research. The aim is to improve computer-assisted and knowledge-oriented decision support with the help of models and methods from statistics and operations research. The papers in the volume are grouped into sections on: symbolic data, concepts and learning; data analysis and applications; computer-assisted decision support - integrating, representing and processing knowledge.