The Boston Gun Project is a problem-solving policing initiative aimed at reducing homicide victimization among young people in the city of Boston. It represented an innovative partnership between researchers and practitioners to assess the city's youth homicide problem and implement an intervention intended to have powerful impacts in the near term. In early 1996, a working group representing a variety of law enforcement and social service agencies implemented an intervention that strategically responded to gang violence, focused enforcement efforts on gun trafficking, and emphasized communication of the strategy to generate deterrence. The intervention is associated with a 60% decline in youth homicide victimization (i.e., two fewer victims per month). There are smaller declines in other measures of violence. The decline in youth homicide is sharp and occurs coincident with the introduction of the intervention. Competing hypotheses appear unable to account for the decline.