Across the United States, policymakers, practitioners, and communities are seeking ways to reduce the lethal violence highly concentrated in a relatively small number of urban neighborhoods. With funding from the John D. and Catherine T. MacArthur Foundation, the National Network for Safe Communities (NNSC) collaborated with the Chicago Police Department (CPD) and other city stakeholders to implement the Chicago Violence Reduction Strategy (VRS), beginning in 2009. Chicago VRS identifies and targets street groups disproportionately responsible for gun violence and works to deter additional violence using a three-pronged strategy: criminal justice sanctions, community moral suasion, and social services provision. The intervention includes call-in meetings in the targeted police districts, during which identified group members are put on notice by VRS partners—including top leadership from CPD, federal and state prosecutors, and credible community messengers—that although they are valued community members, gun violence must stop, and that street groups represented in the meeting that continue to be involved in shootings will be the target of coordinated enforcement actions. Researchers at the Urban Institute and Yale University, in partnership with NNSC, conducted a comprehensive, mixed-methods, quasi-experimental outcome and impact evaluation of Chicago VRS funded by the MacArthur Foundation. The evaluation began in November 2011, seeking to determine whether and how Chicago VRS affected group member–involved violence and how the intervention may have been related to perceptions of group members, community residents, and police officers.