This article discusses selected reference group-based social influence processes as they may relate to AIDS risk and APB. A model is proposed that suggests that when social network or reference group norms and values are inconsistent with APB, the network will engage in normative and informational social influence processes that inhibit prevention and promote risk behavior. By contrast, when network or reference group norms and values are consistent with APB, the group will exert normative and informational social influence supportive of APB, which will result in higher APB and less risk behavior. Initial data are presented that corroborate several of the assertions of the model, and there is a discussion of some of its practical implications for increasing APB and decreasing risk exposure. (Author abstract)