Youth violence continues to be a serious and too prevalent problem in the United States. There is increasingly compelling evidence that the exceptionally high levels of mortality are linked to access to guns by youth. There is also evidence that youth violence occurs in multiple forms and that these differing forms call for different prevention strategies. Some youth violence is situational, some is best understood within its relationship context, some occurs as part of a predatory criminal activity, and some seems to be the result of serious psychopathology. This paper provides a review of the current understanding of the epidemiology of youth violence in the United States, applies a developmental-ecological perspective to risk, reviews the empirical support for differing prevention approaches, and suggests practice, research, and policy implications of this knowledge base.