Samples of gang members were developed in four U.S. communities: Denver and Aurora, Colorado; Broward County, Florida; and Cleveland, Ohio. Interviewers at each site were trained to use an interview instrument developed for the study. Interviews were conducted with 187 gang members. The findings showed that those who joined gangs tend to begin their gang association at about age 13, join about a year later, and get arrested about the same time they joined the gang. This finding underscores the highly criminogenic nature of gangs and the importance of gang resistance education programs and other primary and secondary prevention efforts that target preteens. The data showed that youth can refuse to join gangs without incurring a substantial risk of physical harm. Since primary prevention and early intervention efforts will not deter all youth from associating with gangs, communities must address the brief "window of intervention" that opens in that year between first association with the gang and first arrest. Crimes especially associated with gangs are assaults that involve rival groups; auto theft and credit card theft; carrying concealed weapons; taking weapons to school; drug trafficking; drive-by shootings; and homicide. Gangs should be viewed as a symptom of more complex and pervasive problems in society. These problems require an integrated, coordinated, and carefully developed youth policy. Such a policy must be accompanied by strategies for developing healthy communities in which youth can develop into responsible and productive citizens. 5 tables and 25 notes