Objective: Research has shown associations between college women's alcohol and/or drug consumption and the risk of sexual assault, but few studies have measured the various means by which sexual assault is achieved. Participants: The authors' Campus Sexual Assault Study obtained self-report data from a random sample of undergraduate women (N = 5,446). Methods: The authors collected data on sexual assault victimization by using a cross-sectional, Web-based survey, and they conducted analyses assessing the role of substance use. The authors also compared victimizations before and during college, and across years of study. Results: Findings indicate that almost 20% of undergraduate women experienced some type of completed sexual assault since entering college. Most sexual assaults occurred after women voluntarily consumed alcohol, whereas few occurred after women had been given a drug without their knowledge or consent. Conclusions: The authors discuss implications for campus sexual assault prevention programs, including the need for integrated substance use and sexual victimization prevention programming. (Contains 2 figures and 1 table.)