The author found gang violence levels high in New York, Chicago, Los Angeles, Detroit, Philadelphia, and San Francisco in the 1970's. He estimated the youth gang population in these cities as ranging from 760 gangs and 28,500 members to 2,700 gangs and 81,500 members. City government statistics showed 525 gang-related murders during the 3-year period from 1972 through 1974. Of the 15 largest metropolitan areas, local professionals interviewed directly reported problems with youth gangs in all but five. Gang members of the 1970's were predominantly male, ranged in age from 10 to 21 years, originated in low-income communities, and included primarily members of ethnic groups most heavily represented in lower educational and occupational categories. Gang violence appeared to be motivated by a desire for material gain and a related desire to exert control over public facilities and resources. Probably the single most important development affecting gang member violence during the 1970's was an extraordinary increase in the availability and use of firearms to commit violent crimes. Methods used in the national study of youth gangs and groups are described. The gang survey interview guide and sources of data on the number of gangs are appended. 27 tables