Regarding gender difference for physical aggression, men reported significantly higher levels of acceptability for both proactive and reactive physical aggression than women. Contrary to predictions, however, there were no significant gender differences for functions of relational aggression (i.e., damage or threat of damage to friendly interactions or any interactions with a person or persons). This finding may be explained by older adolescent men having learned that more covert aggressive behaviors have less social and legal costs compared to physical aggression. Future research is needed to test this theory, as well as whether relational aggression, compared to physical aggression, is more characteristic of women than men at an earlier age. Impulsivity was linked with all subtypes of aggression. In addition, there was an association between all aggression subtypes and normative beliefs about circumstances and scenarios that warrant proactive and reactive violence. These findings emphasize the need for intervention and prevention efforts that target functions as well as forms of aggressive behavior across childhood and adolescent development. Hostile attribution biases--i.e., attitudes and beliefs that justify aggression of any form against persons and groups with particular physical or belief characteristics--should be a particular focus for preventive intervention. An ethnically diverse group of 165 emerging adults completed a battery of self-report instruments that measured aggression and social behavior, impulsiveness, attributions of aggressive intent in various scenarios, and normative beliefs associated with subtypes of aggression. 3 tables, 50 references, and appended examples from the Normative Beliefs of Subtypes of Aggression Scale