The German council movements arose through mass strikes and soldier mutinies towards the end of the First World War. They brought down the German monarchy, founded several short-lived council republics, and dramatically transformed European politics. Building Power to Change the World reconstructs how participants in the German council movements struggled for a democratic socialist society. It examines their attempts to democratize politics, the economy, and society through building powerful worker-led organisations and cultivating workers' political agency. Drawing from the practices of the council movements and the writings of theorists such as Rosa Luxemburg, Anton Pannekoek and Karl Kautsky, Building Power to Change the World returns to their radical vision of a self-determining society and their political program of democratization and socialization. It presents a powerful argument for renewed attention to the political theories of this historical period and for their ongoing relevance for democratic politics today.