Over the past two decades governments worldwide have begun to take action to correct gender disparity in representative bodies, resulting in drastic increases in women’s numeric representation. It is unclear, however, how these increases influence legislative behavior. This research contributes to our understanding of how increases in women’s numeric representation influences substantive representation of women. I collected an original dataset to examine this relationship across twenty-three subnational Argentine legislatures over eighteen years. This project represents one of the first empirical efforts to examine women’s substantive representation over a large number of legislatures over a long duration of time. A key piece of the puzzle is to understand if female exhibit distinct preferences from their male colleagues. The second chapter of the dissertation uses a new data set of ideal point estimates recovered from cosponsorship data to examine gender differences in legislative preferences. I find strong evidence to suggest women display different legislative preferences than their male colleagues. Chapter three investigates how increases in women’s numeric representation influence women’s legislative behavior. Previous research suggests that increasing women’s numeric representation should enhance the probability that women work together to pursue common legislative agendas. Yet, I demonstrate that as the percentage of women in the chamber increases, women are increasingly less likely to work together. I argue that this unexpected finding can be explained by considering how institutions shape women’s legislative incentives. In chapter four, I develop theoretical expectations about the conditions under which increases in the proportion of female legislators, in combination with institutional arrangements, will foster or stifle women’s opportunities and incentives to represent women’s interests. The chapter provides strong empirical support for the hypothesis that women behave differently conditional on institutional incentives. These findings imply that understanding institutions is key to understanding how and when female representatives will stand for women. Taken together, this dissertation makes an important contribution to our understanding of how changes in the proportion of female legislators and differences in institutional contexts shape women’s legislative behavior.