Scott H. Decker is Curator's Professor of Criminology and Criminal Justice at the University of Missouri-St. Louis. He has been involved in research about gangs and gang intervention programs since 1988. He is the author of Policing Gangs and Youth Violence (2002), co-author with G. David Curry of Confronting Gangs: Crime and Community (2002) and co-author with Richard T. Wright of Armed Robbers in Action: Stickups and Street Culture, and Burglars on the Job: Streetlife and Residential Break-ins. Frank M. Weerman is researcher at the Netherlands Institute for the Study of Crime and Law Enforcement in Leiden. He has been involved in several research projects in youth crime, and has written extensively about explanations for delinquent behavior and co-offending. He is currently conducting a large longitudinal research project on the role of delinquent peers and peer networks.