KLAUS HURRELMANN is Professor of Sociology and Health Sciences, Director of the Research Center for Prevention and Intervention, and Dean of the School of Public Health at the University of Bielefeld. He has won several Senior Science awards from the German Research Association, and his numerous publications include the International Handbook of Adolescence (Greenwood, 1994).ULRICH LAASER is Professor of Social Medicine and Epidemiology at the School of Public Health at the University of Bielefeld. He is also Director of the Institute of Population Research and Social Policy in Bielefeld. From 1993 to 1995 he was President of the Association of Schools of Public Health in the European Region.