Cities are where the policy and practice of citizen security are determined. Although national and subnational strategies are essential to scaling-up crime prevention, cities are where they are put into practice. Because of the way they bring opportunities and risks into focus, cities are natural laboratories of policy innovation to prevent and reduce violence. Some of the most remarkable progress in homicide reduction, crime prevention and public safety in recent decades has occurred in large and medium-sized cities, especially in Latin America and the Caribbean.