Gang membership has long been understood to have a disruptive influence on adolescent development and to contribute disproportionately to the rate of delinquent crime. The nature of the impact, and the long-term effects on individuals, have not been well understood. This book uses longitudinal data to examine the developmental consequences of gang membership, and its longer term influence on the life course. This longitudinal approach is made possible by data from a study of antisocial behavior, The Rochester Youth Development Study, which followed one thousand adolescents through their early adult years. The subjects include delinquents who were gang members and others who were not, allowing the authors to compare motives, patterns of behavior, and recurring problems with caregivers and the law, education, peer relations, and career paths. The findings indicate that multiple developmental deficits lead to gang membership and that membership leads to an increase in delinquency.