The study focused on the largest gang in each of the jurisdictions studied. Independent variables were city size, number of gangs in the city, the size of the largest gang in the city, the presence of out-of-town affiliations, the gang's length of operation, and its organization sophistication. The impact of these forces on the frequency of violence by the city's largest gang against rival gang members and against citizens not involved in gang activities was analyzed separately. Questionnaires were mailed to 131 municipal police departments in nine States. Violence was selected as the independent variable. Correlations provide some support for the idea that sophisticated big city gangs are colonizing smaller municipalities. Hierarchical regressions show that internecine violence may have somewhat different causes than violence directed towards nongang members. The number of gangs in a jurisdiction was significantly related to both forms of violence, but other variables had differing effects when the two types of violence were examined separately. The authors suggest a developmental scheme for gangs that explains many of these tentative findings and may help to predict future directions for this emergent form of organized crime. 2 tables and 51 references