In this Handbook a number of international gender scholars explore the third ‘wave’ of research about gender, diversity and federalism. It focuses on how institutions, ideas and practices affect, and are affected by, gender regimes as well as territorially and non-territorially organized diversities, including minority ethnicities, ‘race’, religious and sexual minorities. In recent decades, scholarship examining the intersections between gender, diversity and state architectures in federations progressed through several earlier ‘waves’. In the first wave, starting in the 1980s, feminist political scientists and legal scholars began exploring if federal systems were good or bad for women in reference to their ability to make claims against the state, usually coming to the unsatisfying conclusion that ‘it depends’. Most of these early inquiries referred to older federations, such as Australia and Canada. A second wave of gender/federalism research started around 2000. Building on earlier inquiries, feminist scholars of federalism explored if and how federal systems were gendered and what this means for women’s advocacy, organization and citizenship. But they often failed to recognize the changing natures of federations and how actors such as women’s movements can reshape architectural arrangements and institutional opportunities.