The struggle over defining, naming, and using concepts is central to many political conflicts. In this original account of conceptual activism, Davina Cooper asks how new conceptual meanings are made, used, held, and experienced. Drawing on theoretical and empirical research, she analyzes the high-profile contemporary conflict in Britain over sex and gender. Here policymakers, regulatory bodies, community organizations, and academics fight to draw and redraw categories and their boundaries in a struggle that has spread across the census, speculative law reform, equality governance, and more. To understand the techniques and challenges that the advancement of new and controversial meanings faces, Conceptual Activism offers an innovative account of concepts and how meaning is reorganized in conditions of resistance, attentive to concepts' materiality, plasticity, force, and unexpected encounters. As sex and gender meet economy, property, play, and activism, Cooper demonstrates how and why academic work should engage in conceptual activism.