Given the slow speed by which women’s representation in political bodies has increased, there have been amplified calls for more effective measures to reach gender balance in political institutions. Gender quotas represent one such measure. In fact, since 1995, gender quotas have rapidly spread across the world (Dahlerup, 2006; Dahlerup & Freidenvall, 2005; Krook, 2009; Lépinard & Rubio-Marín, 2018). Today, more than one hundred countries have adopted gender quotas to “fast-track” women’s representation in elected bodies of governments, ranging from reserved seats, legislated candidate quotas, and party quotas at national and/or subnational levels. While gender quotas vary in terms of design, where they are used, and to what extent they have achieved their objectives, they represent a major electoral reform, changing the dynamics of candidate selection and the traditional norms of politics as a male business.This chapter addresses this global phenomenon – this gender quota revolution – by focusing on three key aspects: What are gender quotas, why are they adopted, and how have they been implemented (effect). The ways in which they have contributed to the diffusion of quotas in other arenas (spill-over) are also addressed. The chapter is based on our extensive research in the field over the past 20 years, as well as additional research by colleagues across the world. In general, gender quotas are a mounting research area and subject to scientific discussions in dissertations, journal articles, and books, as well as at numerous conferences (Dahlerup, 2019).