https://doi.org/10.1177/10659129211028290 Political Research Quarterly © 2021 University of Utah Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/10659129211028290 journals.sagepub.com/home/prq How electoral institutions incentivize substantive repre- sentation is a crucial question for democratic governance, particularly for traditionally underrepresented groups. This article examines the extent to which proportional representation (PR) and single-member districts (SMDs) encourage lawmakers to pursue legislation on behalf of women, a historically marginalized constituency in most developed democracies. We show that electoral system conditions the relationship between legislator gender and the representation of women, affecting the sponsorship and passage of women’s issue bills introduced by legisla- tors of both genders. Theories of legislative institutions suggest that SMDs encourage representation of the district median voter, result- ing in lawmakers converging on majority-oriented policy positions, at both the district and national levels (Ansolabehere and Jones 2010; Carson et al. 2010). Members elected through PR, seeking to be responsive to the party organiza- tion and its leadership, and free from needing to appeal exclusively to the median, better represent marginalized groups (Blais and Massicotte 2002; Jones et al. 2002; Shugart, Valdini, and Suominen 2005). We extend these theories to the study of gender representation. While previ- ous examinations of the link between electoral systems and gender politics have focused exclusively on women or on specific legislative activities such as bill sponsorship (Caul Kittelson and Schwindt-Bayer 2012; Höhmann 2020; H. O. Jeong 2019; M. Jeong and Lee 2020; Y.-I. Lee 2019; Matland and Studlar 1996; Shim 2021; Thames 2017), our theory and data allow for a comparison of both bill sponsorship and pas- sage activities across gender and electoral system. This approach allows us to understand the conditions in which electoral systems incentivize not only women but also men to support women’s issue bills and bring about favorable policy change. Using machine learning to classify legislative topic areas, we develop a new dataset of bill introductions in the Korean National Assembly from 2004 through 2016 to compare the legislative behavior of women and men elected under each of the country’s electoral systems. 1028290PRQ XX X 10.1177/10659129211028290Political Research QuarterlyKweon and Ryan research-article 2021 1 Department of Political Science and Diplomacy, Sungkyunkwan University, Seoul, South Korea 2 Utah State University, Logan, USA Corresponding Author: Josh M. Ryan, Department of Political Science, Utah State University, 0725 Old Main Hill, Logan, UT 84322, USA. Email: josh.ryan@usu.edu Electoral Systems and the Substantive Representation of Marginalized Groups: Evidence from Women’s Issue Bills in South Korea Yesola Kweon 1 and Josh M. Ryan 2 Abstract How do electoral rules shape the substantive representation of traditionally underrepresented groups? Using an original dataset of introduced and passed bills in the Korean National Assembly, which has both single-member districts and proportional representation, we examine the extent to which institutions condition the relationship between lawmaker gender and the substantive representation of women. While women lawmakers engage in higher levels of substantive representation of women, proportional representation allows both women and men to introduce more women’s issue bills than their counterparts elected through single-member districts. Furthermore, legislators elected through proportional representation are more effective at achieving passage of women’s issue legislation when compared with those elected in single-member districts, and this effect is especially pronounced for men. Our findings show that electoral systems matter for the representation of marginalized groups and that proportional representation systems allow both female and male politicians to increase their substantive representation of women. Keywords electoral rules, single-member representation, proportional representation, women’s representation, legislative productivity, comparative institutions 2022, Vol. 75(4) 1065–1078 Article