Despite years of evidence showing that men are typically considered to be more appropriate and effective in leadership positions than women, a recent debate has emerged over the potential existence of a female leadership advantage in certain contexts (Eagly & Carli, 2003a; Vecchio, 2003; Eagly & Carli, 2003b). This meta-analysis aims to contribute to this debate in the literature by quantitatively summarizing gender differences in leadership effectiveness using 99 independent samples from 95 studies. Results show that when all leadership contexts are considered together there is a non-significant gender difference in leadership effectiveness. Additionally, this study examines the influence of contextual moderators developed from role congruity theory (Eagly & Karau, 2002) and some competing theoretical frameworks. Overall, the findings support the core tenets of role congruity theory--that prejudice against female leaders can vary depending on a variety of features of the leadership context and characteristics of the perceivers of the leader's effectiveness. However, some of the hypotheses proposed by role congruity theory were only partially supported. The results of this meta-analysis point to ways in which the theory can be updated and expanded by taking into account findings supported by other theories presented in the literature on gender and leadership. Finally, this meta-analysis provides important practical implications for reducing the barriers women may face throughout the leadership labyrinth as they pursue the most elite leadership positions.