"Unite our country's workmen". The Situationist International was formed at a meeting in the Italian village of Cosio d'Arroscia on 28 July 1957 with the fusion of several extremely small artistic tendencies, which claimed to be avant-gardistes: Lettrist International, the International movement for an imaginist Bauhaus (an off-shoot of COBRA), and the London Psychogeographical Association. The groups came together intending to reawaken the radical political potential of surrealism. The group also later drew ideas from the left communist group Socialisme ou Barbarie.

The most prominent French member of the group, Guy Debord, has tended to polarise opinion. Some describe him as having provided the theoretical clarity within the group; others say that he exercised dictatorial control over its development and membership; yet others believe that he was a powerful writer but a second-rate thinker. Other members included the Dutch painter Constant Nieuwenhuys, the Italo-Scottish writer Alexander Trocchi, the English artist Ralph Rumney (sole member of the London Psychogeographical Society, Rumney suffered expulsion relatively soon after the formation of the Situationist International), the Scandinavian artist Asger Jorn (who after parting with the SI also founded the Scandinavian Institute for Comparative Vandalism), the veteran of the Hungarian Uprising Attila Kotanyi, the French writer Michele Bernstein, and Raoul Vaneigem. Debord and Bernstein later married.