An introduction to the thought of Pierre-Joseph Proudhon, the first person to declare themself an anarchist. Available in English for the first time, Proudhon’s Sociology is the landmark statement on Pierre-Joseph Proudhon’s thought. While interest in Proudhon’s work has undergone a revival in the last couple of decades in the English-speaking world, his theories about society remain little known. Ansart’s book renders the complexity of Proudhon’s thought intelligible and emphasizes how Proudhonian ideas remain relevant today. Ansart explores the similarities between Proudhon and Marx’s thought, including the influence that Proudhon’s economic writings and theories of the state had on Marx. A year before the publication of Sociologie de Proudhon (1967), Henri Lefebvre published Sociologie de Marx as part of the same academic series. Both indispensable books, which were available to French students at the time of the strikes of May–June 1968, had a real impact on the theoretical education of that generation—and on generations since. This English-language edition contains an introduction by René Berthier, annotations by the translators and editor, and an additional piece by Ansart titled “Proudhon Throughout History.”