This volume contains revised versions of selected papers presented dur- ing the 23rd Annual Conference of the German Classification Society GfKl (Gesellschaft fiir Klassifikation). The conference took place at the Univer- sity of Bielefeld (Germany) in March 1999 under the title "Classification and Information Processing at the Turn of the Millennium." Researchers and practitioners - interested in data analysis, classification, and information processing in the broad sense, including computer science, multimedia, WWW, knowledge discovery, and data mining as well as spe- cial application areas...