Two studies test the hypotheses that men, relative to women: 1) see manhood as a more elusive, impermanent state than womanhood, and 2) understand aggression as a means of proving or re-establishing threatened manhood, but not threatened womanhood. In Study 1 (N = 175 Northeastern U.S. undergraduates), men’s (but not women’s) sentence completions revealed tendencies to define manhood by actions and womanhood by enduring traits. In Study 2 (N = 113 Southeastern U.S. undergraduates), men were more likely than women to explain a man’s physical aggression in primarily situational terms, whereas men and women did not differ in the attributions they made for a woman’s physical aggression. Results suggest that men perceive active and aggressive behaviors as integral parts of manhood and its defense.