Critical mass theory argues that women's numbers are a major cause of women's status and authority in a group. Applications of the theory to political settings have yielded mixed support for the theory. We unpack one mechanism that can explain when, why, and how numbers aid women. That mechanism is the norm of communication during group discussion. Our focus is on how women build or lose authority while they interact with men. We argue that numbers – and group procedures – shape norms that advance or hinder women's authority. Women's authority in turn affects the group's decision about economic redistribution – the higher the women's authority, the higher the group's generosity to the poor. We suggest that future work further explore how rules and norms affect women's status in a group by equalizing their participation and influence, with the ultimate goal being equal gender authority.