The rise of gender expertise and gender experts as a new profession is a significant and highly controversial phenomenon of contemporary feminist politics. This introductory article provides a contextualisation of this phenomenon, a short review of the literature and a theoretical specification of gender expertise, drawing on insights from the professionalisation and expertise literature. We highlight the importance of studying the politics of gender expertise and interrogate the type of knowledge that it constitutes and its relationship to policy and politics (including feminism). The special issue as a whole shows the varieties and complexities of gender expertise, what it makes possible and what it forecloses, and the disruptions it produces. The contributions adopt different approaches to show: how gender expertise is rent with tensions and divisions; how it is constrained within institutions, networks and policies; and how it produces multiple and sometimes unintended outcomes with powerful political effects.