Paul E. Tracy is a criminologist who specializes in the study of crime and delinquency and policy developments in the criminal and juvenile justice systems. He holds a faculty appointment as Professor of Criminology in the School of Criminology and Justice Studies at the University of Massachusetts Lowell, USA. His research interests focus on the measurement and analysis of juvenile delinquency careers, legal and policy issues in juvenile justice, prediction models of criminal careers, and drug prohibition policy. He is a recognized expert in the application of longitudinal research designs to the study of delinquent and criminal careers. His study of a large Philadelphia birth cohort of 27,160 people is the largest study of delinquency and crime ever conducted. He also carried out the first large-scale delinquency study in Puerto Rico, and has published ten books and numerous articles in scholarly journals.Danielle Marie Carkin is an Assistant Professor of Criminology at Stonehill College, USA. Her research focuses on juvenile delinquency and justice, criminal careers, and co-occurring disorders among inmates. She has published numerous papers in American Journal of Criminal Justice, Journal of Law and Criminal Justice, and Journal of Psychology, among others. She has also co-authored pieces in the Routledge Handbook of Social, Economic, and Criminal Justice and Society, Ethics, and the Law: Text Reader.