Many efforts to prevent men's sexual violence have focused on changing some men's belief that most other men approve of rape-supportive attitudes and behaviors, when in fact this is not true. A person's beliefs about the attitudes and behaviors of others, and the way those beliefs influences that person’s own attitudes and behaviors, are called social norms. Changing social norms around sexual violence is an important part of prevention effots. This article describes a survey of the social norms held by college students at a mid-Western university in the United States, and provides extensive background information about social norms research and prevention applications.