Aggressive children are known to have friends. However, less is known about the impact of aggression on friendship development and how this can differ for overt and relational (i.e., the forms) and instrumental and reactive (i.e., the functions) aggression. This longitudinal study utilized the forms and functions perspective on aggression to assess social selection and influence in adolescents' (N = 337, 12-14 years) friendship networks. Instrumentally and relationally aggressive peers became mutual friends with similar peers. Influence effects were observed in all types of aggression except overt aggression, suggesting that instrumental, reactive, and relational aggression may be the most susceptible to social influence. The findings are discussed in terms of theoretical and methodological implications for the study of aggression and adolescent friendships.