In 1980, 351 persons died in Los Angeles County due to gang violence; in 1991, this figure climbed to 795. Few youths are forced into gangs; rather, young people seek out gang membership to associate with others who have similar background deficiencies. Because gangs are becoming increasingly mobile and frequently direct violence at law enforcement personnel, police officers must develop effective tactical approaches to gang prevention. The manual covers the sociology of street gangs, gang recruitment, causative factors, gang communication and leadership, and gang-related crime and violence. Manual sections focus on Hispanic, black, white, and Asian gangs and also on female gangs. Responses of the Los Angeles County Sheriff's Department to criminal street gangs are reviewed, and the development of legal expertise and strategies to deal with street gangs is emphasized.