Following a brief review of the history of the juvenile justice system, psychological theories of juvenile delinquency are reviewed. Research into factors in juvenile delinquency then is summarized in the areas of demography (age, gender, ethnicity, socioeconomic characteristics), and social ecology. Four major patterns of delinquent behavior are described. Also reviewed is empirical evidence for a relationship between delinquency and intelligence, personality, biogenetic factors, and family characteristics and functioning. Reviews of outcome studies examine the effectiveness of institutional treatment; community-based interventions; and behavioral, cognitive, and psychodynamic individual, group, and family interventions. Factors predictive of later delinquency (including chronic and violent offending) and adult criminality are identified, and their implications for juvenile delinquency prevention are discussed. Also reviewed are institutional and community prevention strategies. Finally, methodological issues in outcome and process evaluations of treatment effectiveness are addressed. Chapter references; author and subject indexes.