Rolf Loeber, Ph.D., is Distinguished University Professor of Psychiatry, and Professor of Psychology, and Epidemiology at the University of Pittsburgh and Professor of Juvenile Delinquency and Social Development at the Free University, Amsterdam, Netherlands. He is Co-director of the Life History Program. 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.