Data were analyzed to identify groups at greatest risk of homicide victimization, situational and interpersonal characteristics associated with homicide, changes in the risk of homicide victimization over time, and patterns of alcohol and drug use by homicide victims. Data were obtained from internal records of the Los Angeles Police Department and the Medical Examiner-Coroner's Office. Rates were calculated from the population estimates of the U.S. Bureau of the Census. Implications of the findings for research and prevention focus on crime-related violence, gang violence, domestic violence, friend/acquaintance violence, alcohol use, and firearms use. The study recommends that prevention efforts target high-risk groups and the weapons, relationships, and circumstances associated with homicide in these groups. Appendixes contain examples of homicide case summaries, the data collection protocol, a discussion of the validity of population data, and a list of tables. A glossary and 77 references.