Observers have found it helpful when studying adolescent behavior to define three stages: early (12-15 years), middle (15-17 years), and late (17-19 years). Early adolescence is the time when children begin the separation process from their parents and other adults, but still retain many dependent needs. Middle adolescence, the age of the adolescent subculture, is a period in which the importance of peer group pressures increases. Late adolescence is when the adolescent becomes more self-sufficient physically, emotionally, and financially. Gangs develop during the years between childhood and adulthood when individuals are looking for an identity, a peer group, and a purpose. Gangs occur most commonly in cities with large minority populations, where the population has not been integrated into the larger U.S. environment. Although gangs tend to be identified with poor black or Hispanic neighborhoods and with dysfunctional families, gangs also occur in middle class and white societies. There are many similarities between gangs, high school athletic teams and clubs, and adolescent peer groups. Each satisfies adolescents' need to belong to a group that will offer acceptance and help them develop an identity. Gang members are no different from nongang teenagers in terms of developmental needs and goals. Frustrated with their world, however, they may develop alternative antisocial solutions to accomplish the same goals as nongang teens. A history of the gang movement is provided, along with a description of gang structure. Research on gang formation in Chicago and Southern California is presented to illustrate demographic characteristics of the gang phenomenon. A review of literature on female participation in gangs is presented, and current theories on potential solutions to the problem of teenage gangs are discussed. 60 references