The sociological tradition of socialization/normative influence involves a set of theoretical orientations that view interpersonal relations as the medium for normative influence on attitudes and behavior. These orientations encompass symbolic interaction theory, reference group theory, and related conceptions of social influence. A second sociological tradition that bears upon peer influence is the social ecological approach elaborated in the routine activity perspective, which views interpersonal relations as part of the process by which social structure shapes the spatial and temporal activities of social life, thereby increasing opportunities for some behaviors and decreasing opportunities for other behaviors. In exploring empirical data relevant to these 2 perspectives, this study used findings from the Add Health survey, which involved a nationally representative sample of adolescents in grades 7 through 12, who were attending 132 schools selected with unequal probability in 1995-96. To measure the social networks of the students at each school, the survey asked students to nominate up to five of their closest female friends and five of their closest male friends. By linking these nominations to the friends' responses about their own involvement in deviant activities, researchers constructed network-based measures of peer relationships and peer characteristics. The study found support for both the socialization and opportunity models, as adolescents were found to engage in higher rates of delinquency if they had highly delinquent friends and if they spent a lot of time in unstructured socializing with friends. Four parameters for peer influence are identified. 3 tables, 13 notes, and 79 references