Psychologists believe they can intervene effectively in the lives of young people to reduce or prevent their involvement in violence. In addition, psychologists generally agree that one of the strongest predictors of an individual's risk of perpetrating violence is a history of aggressive behavior as a child. To understand violence causes, it is necessary to focus on early childhood experiences and on developmental pathways that lead to involvement in violence in later life. Factors contributing to aggression and violence are discussed, as well as the incidence of violence in the United States and psychology's contribution to understanding violence. Attention is paid to the etiology of violence, ethnic group violence, violence among selected vulnerable populations (girls and young women, lesbians and gays, bisexual youth, and children with disabilities), societal influences on youth violence, violence prevention and intervention, and research and public policy needs related to violence. The authors conclude that interpersonal violence is one of the most prevalent, socially destructive, and problematic health risks faced by Americans and that effective interventions should involve families, schools, communities, media, and health care professionals. 104 references