This study examined prospective associations between late adolescents' friendships and substance use (alcohol, marijuana, tobacco) using a stochastic actor-based modeling approach and the moderating role of popularity. Participants were 450 adolescents (53% female, M age = 15.5 years) who completed surveys in grades 10 and 11. Results of a single multivariate model indicated that peer selection based on similar tobacco use was a more robust predictor of changes in friendship than selection based on similar alcohol and marijuana use; and peer socialization of alcohol use predicted more changes in adolescent-drinking behaviors. Popularity moderated selection based on alcohol use; popular adolescents were more likely to select friends with high levels of drinking behaviors. Popularity did not moderate peer socialization.