This chapter explores the foundational richness and broad application of the gender equality regime as a core concept in research on the European Union (EU). The notion of a EU gender equality regime emphasizes the importance of supranational-level gender policies but also allows for the consideration of regional or national-level diversity. Less a theory than a heuristic framework, it permits analyzing policies, actors, and institutions across time and place. The peak of optimism and support for the EU and its gender equality initiatives can be situated between the Amsterdam Treaty in 1997 and the following decade, when EU membership grew to 28 states. The literature on gender more broadly is multi-disciplinary, highly productive, and extensive. The gender regime can be considered one of the most employed frameworks for the analysis of gendered policy and institutions originating in feminist sociology and political science.