Socialisme ou Barbarie (French for Socialism or Barbarism) was a French-based radical libertarian socialist group of the post-World War II period whose name comes from a phrase Friedrich Engels used, which was cited by Rosa Luxemburg in the 1916 essay The Junius Pamphlet. It existed from 1948 until 1967. The animating personality was Cornelius Castoriadis, also known as Pierre Chaulieu or Paul Cardan.
The group originated in the Trotskyist Fourth International, where Castoriadis and Claude Lefort constituted a Chaulieu–Montal Tendency in the French Parti Communiste Internationaliste in 1946. In 1948, they experienced their "final disenchantment with Trotskyism", leading them to break away to form Socialisme ou Barbarie, whose journal began appearing in March 1949. Castoriadis later said of this period that "the main audience of the group and of the journal was formed by groups of the old, radical left: Bordigists, council communists, some anarchists and some offspring of the German 'left' of the 1920s
They developed parallel to, and were in dialogue with, the Johnson–Forest Tendency, which developed as a body of ideas within American Trotskyist organisations. One faction of this group later formed Facing Reality. The early days also brought debate with Anton Pannekoek and an influx of ex-Bordigists into the group.
The group was composed of both intellectuals and workers, and agreed with the idea that the main enemies of society were the bureaucracies which governed modern capitalism. They documented and analysed the struggle against that bureaucracy in the group's journal. The thirteenth issue (January–March 1954), as an example, was devoted to the East German revolt of June 1953 and the strikes which erupted amongst several sectors of French workers that summer. Following from the belief that what the working class was addressing in their daily struggles was the real content of socialism, the intellectuals encouraged the workers in the group to report on every aspect of their working lives.