This article reviews the definitions and epidemiology of the several forms of interpersonal violence in family and intimate relationships. Interpersonal violence includes both fatal and nonfatal violence where physical force, or other means, is used by one person with the intent of causing harm, injury, or death: family violence includes child maltreatment, adult intimate-partner violence, and elder mistreatment; abuse refers to a pattern of behaviors organized around the international use of power by one person to control another; and child maltreatment involves the abrogation of adult responsibilities for the care and protection of children, and includes child abuse, child sexual abuse, and child neglect. Violence is a major public health problem in the United States. Half of assault and homicide victims are related to or acquainted with their assailants, as are two-thirds of rape victims. Children and adolescents are at particular risk of violence. The study of interpersonal violence is a complex and evolving held, and is increasingly a part of training and medical practice in academic settings.