Explanations of gang membership were studied in a population of 11,000 secondary school students. Lower self-esteem, perceived academic ability, psychosocial health, and bonds with institutions appeared to precede gang membership (selection model). Greater drug use, greater delinquency, greater fear of harm, and being armed were precursors and consequences of gang membership (facilitation and selection models). “Wannabes” were partway between nonmembers and members. Findings were consistent with gang membership as a result of lack of social integration.