The relations between normative beliefs about different forms of aggression and corresponding aggressive behaviors were investigated in 2 studies of adolescents. In Study 1, we revised an instrument designed to assess normative beliefs about aggression to include beliefs about the acceptability of relational aggression, and we examined the psychometric properties of the instrument. In Studies 1 and 2, the unique associations of normative beliefs about relational and physical aggression with self-reported relational and physical aggression were examined. Findings across both studies revealed that beliefs-behavior associations were specific to aggression forms. In other words, beliefs about relational aggression were uniquely associated with engagement in relationally aggressive acts, whereas beliefs about physical aggression, but not relational aggression, contributed unique information about adolescents' level of physical aggression. No gender effects were found. Results are discussed within a social-cognitive framework, and implications are explored for future prevention and intervention efforts to reduce aggressive behaviors.