Descriptions of self (e.g., "I am dominant") may reflect not only a person's behavioral tendencies but also idiosyncratic definitions of the social concepts and categories being considered. Five studies revealed that participants who differed in their self-ratings along trait dimensions also tended to associate different behaviors and performances with those traits. For example, participants who described themselves as dominant tended to emphasize desirable over undesirable behaviors and characteristics in their definitions of the trait, whereas self-described nondominants highlighted the opposite. Participants' self-ratings on dominance were also influenced by making positive or negative examples of dominant behavior salient to them. Moreover, when participants were induced to shift self-descriptions in self-serving ways, they tended to do so by revising their prototype of the trait in question. Discussion centers on the implications of these findings for the prediction of behavior and the interpretation of some social science results.