Uncovers the neglected theories of the council system in the 20th century Reconstructs the history of the century council system and puts it into dialogue with theoretical formulations of council democracy from Karl Marx to Hannah Arendt Focuses on neglected parts i.e. the council system of the political thought of Castoriadis, Arendt and Lefort, and reinterprets their political thinking in the light of the council system Introduces a novel theoretical vocabulary through which to understand the historical experiences of the council system Contributes to the literature on radical democracy by situating council democracy as an alternative to both liberal democracy and radical democracy Analyses the contemporary relevance of council democracy in the light of the contemporary 'square movements' This book examines the historical emergence of the council system in Russia and Germany by the end of the First World War, reconstructing the intellectual history of council democracy in 20th century political theory, and providing in-depth analysis of council democracy in the political thought of Cornelius Castoriadis, Claude Lefort and Hannah Arendt. Popp-Madsen argues that council democracy can productively be interpreted through the prism of constituent power: the form-giving power of the people to decide on their own institutional forms of political co-existence. Whereas other interpreters of constituent power claim an unbridgeable gap between constituent power and constituted power, this book asserts that council democracy discloses a historically grounded way of institutionalising the constituent power. Council democracy, in this interpretation, becomes a way of controlling the constituent power without completely exhausting it, thereby giving the citizenry continual access to the powers of self-transformation, co-creation and constituent freedom.