David P. Farrington, O.B.E., is Professor of Psychological Criminology at the Institute of Criminology, Cambridge University, and Adjunct Professor of Psychiatry at Western Psychiatric Institute and Clinic, University of Pittsburgh.Â He is co-chair of the U.S. National Institute of Justice Study Group on Transitions from Juvenile Delinquency to Adult Crime and co-chair of the U.S. Centers for Disease Control Expert Panel on Protective Factors against Youth Violence. His major research interest is in developmental criminology, and he is Director of the Cambridge Study in Delinquent Development, which is a prospective longitudinal survey of over 400 London males from age 8 to age 48. In addition to over 500 published journal articles and book chapters on criminological and psychological topics, he has published over 75 books, monographs and government publications.Rolf Loeber is Professor of Psychiatry, Psychology, and Epidemiology at the Western Psychiatric Institute and Clinic, School of Medicine, University of Pittsburgh, and Professor of Juvenile Delinquency and Social Development, Free University, Amsterdam, Netherlands. He is Codirector of the Life History Program and is principal investigator of three longitudinal studies, the Pittsburgh Youth Study, the Developmental Trends Study, and the Pittsburgh Girls Study. He has published widely in the fields of juvenile antisocial behavior and delinquency, substance use, and mental health problems (more than 130 peer-reviewed papers and 90 book chapters and other papers).