What works in preventing and reducing violence among youth? This report draws on the global evidence base of evaluations of existing interventions designed to reduce or prevent violence and identifies those with the greatest evidence of effectiveness. We find six types of interventions for which there is strong evidence of effectiveness in preventing at-risk individuals and offenders from engaging in criminal and violent behavior—cognitive behavioral therapy, multidimensional therapy, drug courts and drug addiction treatment, focused deterrence, controls on the sale and abuse of alcohol, and hot spots policing. A much broader range of interventions have shown less conclusive proof of effectiveness—either because they have not been rigorously evaluated or because evaluations have yielded mixed results. In these cases, we identify the mechanisms that may lie behind potential success and explore how these might be extracted to promote innovative pilots in the Mexican context.