A gang is defined as "any group gathered together on a continuing basis to commit antisocial behavior." Gang typologies are the "traditional" gang, whose heritage can be traced back for generations (Hispanic gangs) and the "transitional gang," which is a relatively new gang that is in the process of becoming a "traditional" gang (black and Asian gangs). A discussion of gang recruitment is followed by an overview of factors that contribute to the formation and continuation of gangs; factors include socioeconomic pressures and family structure. The descriptions of gang structures distinguishes these structures according to Hispanic gangs, black street gangs, Asian gangs, and white gangs. A discussion of the relationship of prison gangs to street gangs notes that although prison gangs are not an extension of street gangs, the majority of prison gang members were, at some time, members of either barrio, ghetto, or motorcycle gangs. A profile of gang activity concludes that the street-gang milieu inevitably leads to violent crime. Other topics considered are gang communication and gang involvement in drug use and trafficking. In countering gang violence, the paper recommends a multifaceted strategy that involves law enforcement agencies, community-based organizations, community leaders, and the business community. Expansion of law enforcement and probation units that specialize in street gang enforcement techniques is proposed.