This volume contains revised versions of 35 papers presented during the 15th Annual Con- ference of the Gesellschaft fiir Klassifikation (GfKl), the German Classification Society. The conference took place at the University of Salzburg (Austria) in February 1991; the local organizer was Prof. Hans Goebl, Director of the Institute for Romance Philology at Salzburg. The scientific program of the conference included about 100 plenary or contributed papers, a lot of software presentations and special (tutorial) courses. Researchers and practitioners interested in data analysis and clustering methods, information sciences and database techniques, or applications in archaeology, biology, criminology, geography, lin- guistics, and medicine had the opportunity to discuss recent developments and to establish cross-disciplinary cooperation in these fields. The conference owed much to its sponsors EMCO Maier GmbH, Hallein, Osterreichisches Bundesministerium fiir Wissenschaft und Forschung, Wien, Osterreichische Forschungsgemeinschaft, Wien, Salzburger Landesregierung, Stadt Salzburg, Multimedia 2000, Salzburg, who helped in many ways. Their generous support is gratefully acknowledged. The volume consists of the three parts - Data Analysis, Classification, - Data Modeling, Knowledge Processing, - Applications, Special Subjects. Arrangement of the papers into the respective parts was supported by the keywords assigned to each paper by authors and referees.