This article conceptualises gender expertise in global governance as a transnational field. We propose two theoretical shifts: a depersonalisation to understand expertise as a field rather than experts as individuals or a group of people; and a re-conceptualisation of expertise from a depoliticised body of knowledge towards expertise as a performative and intrinsically political practice. Drawing on qualitative data, we identify practices of boundary drawing and erasing to analyse three key cleavages of this field: contestations over the boundary between gender expertise and feminism; contestations over scientific epistemologies and authority; and contestations over the logics of (post-)colonial politics surrounding gender expertise.