President Obama's administration has shown a renewed emphasis on evidence-based policy. The President's FY11 budget includes over US$100 million for rigorous evaluations to grow the number of interventions backed by strong evidence of effectiveness. Other efforts focus on increased funding for top tier programmes and practices, evaluation of programmes with some supportive evidence of effects, and testing of innovative programmes that are supported by preliminary research findings.  Youth violence prevention is an area of social and health policy that is ripe for the application of scientific evidence. Youth violence is a significant public health problem: homicide is the second leading cause of death for youth ages 10–24.1 As a result of decades of investment in research by federal agencies, such as the Centers for Disease Control and Prevention (CDC) and the National Institutes of Health, as well as non-profit foundations, a substantial body of scientific evidence has uncovered factors …