‘Socialism’ means different things to different people. The concept denotes a just society in which no individual lacks the basic necessities of life and in which prosperity and knowledge are shared fairly. But opinions on what form such a society should take have always varied widely. Should it be governed centrally? Should it be a federation of small communities? A meritocracy? A democracy? ‘Socialism’ was, and is, a house with many rooms, and as a political movement it has left a deep mark on the past two centuries. These two volumes attempt to provide a – necessarily incomplete – overview of the non-communist aspect of this tradition; the communist aspect is the subject of a separate publication project.