Overclaiming—in which individuals overstate their level of familiarity with items—has been proposed as a potential indicator of positive self-presentation. However, the precise nature and determinants of overclaiming are not well understood. Herein, we provide novel insights into overclaiming through 4 primary studies (comprising 6 samples) and a meta-analysis. Based on past empirical work and theoretical discussions suggesting that overclaiming may be the result of several processes—including an egoistic tendency to self-enhance, intentional impression managing behavior, and memory biases—we investigate various potential dispositional bases of this behavior. We hypothesized that overclaiming would best be predicted by a dispositional tendency to be curious and explorative (i.e., high Openness to Experience) and by a dispositional tendency to be disingenuous and self-centered (i.e., low Honesty-Humility). All studies provided support for the first hypothesis; that is, overclaiming was positively associated with Openness. However, no study supported the hypothesis that overclaiming was associated with Honesty-Humility. The third and fourth studies, where multiple mechanisms were compared simultaneously, further revealed that overclaiming can be understood as a result of knowledge accumulated through a general proclivity for cognitive and aesthetic exploration (i.e., Openness) and, to a lesser extent, time spent in formal education.