Motorcycle gangs have evolved into structured organizations which use their affiliation with motorcycling clubs as a conduit for criminal activities. Such activities include drug offenses, assault, weapons offenses, burglary, and robbery. Drugs increasingly represent the main source of income for motorcycle gangs. Gang violence resulting from internal conflicts, gang rivalries, power struggles, and antagonism toward law enforcement personnel has also escalated. Dominant motorcycle gangs in the United States are described, including Hell's Angels, Pagans, Outlaws, Bandidos, and Sons of Silence. Other major motorcycle gangs are also noted, and geographic locations are identified. A State-by-State review of gangs and gang-related criminal activities is presented, and news articles on gang law enforcement, arrest, and prosecution are included. Figures