This study examined to what extent peer influence explains the development of illegal political behavior controlling for peer selection, legal political peer influence, and gender effects. Late adolescents who filled out questionnaires at two annual measurements were used in a longitudinal social network approach (N = 1006; Mage = 16.62). Results showed that peers' involvement in illegal political behavior predicted adolescents' increases in illegal political behavior. Adolescents did not select other peers with similar illegal political behavior. Nevertheless, adolescents selected peers with similar legal political behavior. Findings were discussed in light of a stage process where adolescents initially chose peers with similar legal political behavior. Subsequently, peers influence adolescents on both legal and illegal political behavior.