Violence among youths is an important public health problem. Between 1985 and 1991, homicide rates among youths 15-19 years of age increased 154% and remain, today, at historically high levels. This paper reviews the major trends in homicide victimization and perpetration among youths over the last decade, the key risk factors associated with violence, and summarizes the many primary prevention efforts under way to reduce violence. Previous research points to a number of factors that increase the probability of violence during adolescence and young adulthood. Some of these factors include the early onset of aggressive behavior in childhood, social problem-solving skill deficits, exposure to violence, poor parenting practices and family functioning, negative peer influences, access to firearms, and neighborhoods characterized by high rates of poverty, transiency, family disruption, and social isolation. Efforts to address some of the primary risk factors for violence are under way across the United States, but evaluations to confirm program effectiveness are needed.