Strangers do not perpetrate the majority of sexual assaults reported to law enforcement in the United States today. In identifying this finding, it is emphasized that the response to sexual assault victims and investigative strategies needs to recognize the unique dynamics of nonstranger sexual assault. The SDPD has spent the past 9 years comprehensively analyzing sexual assaults reported to its Sex Crimes Unit and will continue the effort. The result of this comprehensive analysis was the development of the first national sexual assault training curriculum for law enforcement, produced by the National Center for Women and Policing through a grant sponsored by the U.S. Department of Justice. The criminal justice system's response to a reported sexual assault continues to be challenged and compromised by issues that do not generally apply to other crimes. This chapter begins with a review of the nature of sexual assault and how the understanding and the laws against it have changed in recent years. It then reviews the SDPD's data collection, analysis, and prevention efforts. It concludes by describing an epidemiological study conducted to provide the SDPD Sex Crimes Unit with a better understanding of these crimes in San Diego, identify important differences between stranger and nonstranger assaults, and investigate the factors associated with the law enforcement outcomes of these cases. Figures and references