Peter Weiss, who died in 1982, achieved international recognition as a playwright relatively late in his life – at the age of almost fifty when, in 1964, the Marat-Sade received its premiere in West Germany and in London. Although these productions were followed by a Marxist interpretation in East Germany in the following year, it was Peter. Brook's version for the RSC, later filmed, which shaped most English-speaking theatregoers' perceptions of the play, as a culmination of Brook's exploration of ‘theatre of cruelty’. So what is the philosophy of the Marat-Sade? In this article, John McKenzie, who teaches in the Department of German at the University of Exeter, returns to the statements made by Weiss himself – which, though numerous, were mostly in ephemeral or untranslated sources – and traces the feelings of the playwright as these evolved from the political neutrality of what he called the ‘third standpoint’ to the overtly Marxist position of Weiss's later life.