Anarchism is often assumed to stand outside constitutionalism, yet it forms a significant, if overlooked, tradition of constitutional thought. Addressing global constitutional crises and the impasses of state-centred politics, this book brings anarchism into productive dialogue with constitutional, political and international theory. At its core is a reconstruction of anarchist social theory grounded in an ontology of anarchy shaped by European social science and republican concerns with dividing and balancing power. These ideas were reinterpreted by major anarchist thinkers - from Proudhon to Lucy Parsons, and from Tolstoy to K¿toku Sh¿sui - who advanced decentralised, federalist alternatives to imperial and hierarchical orders. Combining intellectual history with co-produced research alongside anarchist groups, Constitutionalising Anarchy shows how constitutional practices developed within militant labour unions, protest movements and cooperatives across the twentieth century. It reconsiders anarchy, constitutionalism and the possibilities of political organisation. This title is also available as open access on Cambridge Core.