Pierre Joseph Proudhon (1809-1865) is one of the most important French social theoreticians of the nineteenth century. George Woodcock's book, first published in 1956, was the first full-scale biography of Proudhon in the English language. Proudhon's influence on the French Socialist movement was immense and he played a great part in the First International and Paris Commune, in French syndicalism and in contemporary movements for currency reform. Proudhon's significance also reaches forward into the contemporary era, when his massive distrust of the state and his teaching of the need for world federation took on a new importance in a world threatened by the explosive rivalries of giant nationalistic states.