The "homicide differential" refers to the unique and often devastating impact of a homicide on co-victims (friends and family of the deceased). This definition and other definitions of terms related to the prevalence and impact of homicide in the United States are presented. A broad spectrum of data related to homicides in the United States is also presented. This is followed by a section on the unique impact/effects on co-victims of homicide. Homicide includes all deaths caused by willful murder and non-negligent manslaughter. Homicide devastates the lives of those who had strong connections to the victim, including family members, friends, and co-workers. It is important for victim advocates to understand that death by homicide differs from other types of death, and cultural attitudes toward death and spirituality influence societal perceptions of homicide. The unique elements of homicide are the intent to harm/kill the victim, the stigma that often blames the victim for precipitating the homicide, the feeling of isolation and deprivation among co-victims, the stress of associated criminal proceedings, and media attention. A separate section of the paper details the reactions of homicide co-victims. An important stressful experience of homicide co-victims is having to deal with strangers in the criminal justice system who did not know the victim and may have become insensitive to the impact of homicide on co-victims. An overview of effective responses of victim support and advocacy is provided, with attention to mental health services, collaborative responses, and challenges for advocates. 33 notes