Violence is a public health problem that can be understood and changed. Research over the past 2 decades has demonstrated that violence can be prevented and that, in some cases, prevention programs are more cost-effective than other policy options such as incarceration. The United States has much to contribute to-and stands to gain much from-global efforts to prevent violence. A new World Health Organization initiative presents an opportunity for the United States to work with other nations to find cost-effective ways of preventing violence and reducing its enormous costs.