This volume contains revised versions of most of the papers presented at the NATO Advanced Research Workshop 011 Data, Expert Knowledge and Decisions. The meeting took place at the UniversiUit del' Bundeswehr Hamburg in September 1989, with local organization by the Institut fiir Informatik. It was the second of its kind, following a workshop held at the Universitiit Karlsruhe in 1987. The workshop brought together researchers and practitioners illterested in current sophisticated data analysis techniques, recent research on computer-assisted decision sup- port, developments of knowledge-based systems, and--this was one of the main issues of the workshop-cross-disciplinary aspects of these fields. Participants in the workshop represented fifteen countries. The meeting was orgallized together with Edwin Diday, Le Chesnay, France, Phipps Arabie, Champaign, U.S.A., Alain Bultez, Bruxelles, Belgium, Franz-J. Radermacher, VIm, Germany. We all, gratefully, take the opportunity to acknowledge support by Aachener Riickversicherungs- NATO Scientific Affairs Division, gesellschaft , Gesellschaft del' Freunde und Forderer del' Universitiit del' Bundeswehr Hamburg, Hewlett Packard GmbH, Universitiit del' Bundeswehr Hamburg, Nixdorf Computer AG, Freie und Hansestadt Hamburg, which made it possible to stage a meeting of this international character. The volume consists of the three parts - Symbolic Data, Concepts and Learning, - Data Analysis and Applications, - Computer-Assisted Decisioll Support: Integrating, Represelltillg and Processing Knowledge.