This study is the first to comprehensively examine the effect of state anti-bullying laws (ABLs) on youth violence. Using data from a variety of sources – including the Youth Risk Behavior Surveys, Uniform Crime Reports, and newly collected data on school shootings – we find that the enforcement of strict, comprehensive school district anti-bullying policies is associated with a 7 to 13 percent reduction in school violence and an 8 to 12 percent reduction in bullying. Our results also show that anti-bullying policy mandates are associated with a reduction in minor teen school shooting deaths and violent crime arrests. A causal interpretation of our results is supported by falsification tests on older young adults for whom ABLs do not bind.