This work examines the link between descriptive representation and substantive representation: do female legislators, in sharing a common gender identity, promote public policies that improve women's rights and citizens' wellbeing? Mexico and Argentina are ideal case studies. Both countries have gender quota laws, compelling political parties to nominate thirty percent women to closed candidate lists. The countries vary, however, on the proportions of female legislators elected and on institutional support for gender policy. Mexico under- fills its quota, but formalizes women's representation through a Bicameral Commission on Equity and Gender. Argentina, by contrast, over-fills its quota, but lacks those institutional mechanisms that legitimate the development of gender policy. I use quantitative and qualitative data to compare female legislators' and male legislators' interventions throughout the policy process. This data includes an original dataset of bill introduction and bill passage, debate transcripts and policy proposals, over 50 interviews with male and female legislators in both countries, and case studies of successful reforms. I consider constituent demands, as expressed through public opinion, and whether these demands link to legislators' agenda setting initiatives. Next, I determine the frequency of bill introduction across policy areas, and compare this statistic to the frequency of legislative success. Finally, I analyze the implementation of successful policies, to evaluate whether or not material benefits reach female constituents. This dissertation is located at the intersection of the comparative politics literature on legislatures and policymaking, on the one hand, and women and politics, on the other. I find that female legislators, more than male legislators, advocate for policies dealing with health, minority rights, and women's rights; I further find that the vast majority of female legislators adopt progressive positions on women's roles and opportunities. Most importantly, I conclude that legislative institutions and practices--namely gender commissions and women's caucuses- -contribute significantly to whether or not the substantive representation of women unfolds