Interpersonal communication that occurs in everyday settings can have powerful health-related effects, but may tend to go unnoticed by participants and researchers because of its commonality and usualness. Understanding the impact of everyday interpersonal messages on health and risk behaviors is important to health communication, health education, and public health efforts, in part because these messages often function in competition with public health messages and campaigns. Social influence is a useful framework for understanding the roles of everyday interpersonal communication in influencing health and risk.