The current study used an experimental design to evaluate a sexual violence prevention program based on a community of responsibility model that teaches women and men how to intervene safely and effectively in cases of sexual violence before, during, and after incidents with strangers, acquaintances, or friends. It approaches both women and men as potential bystanders or witnesses to behaviors related to sexual violence. Three hundred and eighty-nine undergraduates participated and were randomly assigned to one of two treatment groups or a control group. Results from the research reveal that up to 2 months after participating in either a one- or three-session version of the program, participants in the treatment conditions showed improvements across measures of attitudes, knowledge, and behavior while the control group did not. Most program effects persisted at 4- and 12-month follow-ups. The program appeared to benefit both women and men. Implications and future directions for research are discussed. © 2007 Wiley Periodicals, Inc. J Comm Psychol 35: 463–481, 2007.