United Nations guidelines and principles for intervention in urban areas provide norms and standards for the development of crime prevention strategies and policies. Under these guidelines and principles, effective urban crime prevention strategies require strong leadership from national and local governments; strategic planning based on sound analysis of problems and causes; and comprehensive strategies that include the entire range of services and institutions that affect people’s daily lives. Also recommended are community-based and problem solving policing and strong partnerships between policymakers, service providers, and civil society. Governments must also promote the rights of citizens and work against the exclusion of vulnerable groups from access to economic and social resources. These vulnerable groups include the urban poor, children and youth, women, and racial minorities. With these principles in mind, this paper reports on the apparent increases in violence caused by youth gangs or groups in many countries. Concerns about youth violence and crime in various countries revolve around a number of factors, including the use of alcohol and drugs, access to small arms, links with more organized adult gangs, and the deportation of gang members by the United States to their countries of origin in Central America and the Caribbean. On the basis of many studies in various countries, this paper discusses the variety and composition of youth gangs and their involvement in organized armed violence. This paper also outlines lessons learned from recent practice and evaluation in various countries and presents examples of projects and strategies that have targeted urban youth and gang violence. 47 references