--- - |2 Abstract Research has shown that men tend to emerge as leaders more frequently than women. However, societal role expectations for both women and leaders have changed in the decades since the last empirical review of the gender gap in leader emergence (Eagly & Karau, 1991). We leverage meta‐analytic evidence to demonstrate that the gender gap has decreased over time, but a contemporary gap remains. To understand why this gap in leader emergence occurs, we draw on social role theory to develop a Gender‐Agency/Communion‐Participation (GAP) Model—an integrative theoretical model that includes both trait and behavioral mechanisms. Specifically, we examine a sequence of effects: from gender to agentic and communal personality traits, from these traits to behavioral participation in group activities, and ultimately from participation to leader emergence. The model is tested using original meta‐analyses of the personality and behavioral mechanisms (coding 1,632 effect sizes total). Gender differences in leadership emergence are predominately explained by agentic traits (positive) and communal traits (negative), both directly and through the mechanism of participation in group discussions. In addition, several paths in the theoretical model are moderated by situational contingencies. Our study enhances knowledge of the mechanisms and boundary conditions underlying the gender gap in leader emergence. - Personnel Psychology, Volume 71, Issue 3, Page 335-367, Autumn 2018.