In the general election of 1931, the Labour Party campaigned on the slogan `Plan or Perish'. The party's pledge to create a planned socialist economy was a novelty, and marked the rejection of the gradualist, evolutionary socialism to which Labour had adhered under the leadership of Ramsay MacDonald. Although heavily defeated in that election, Labour stuck to its commitment. The Attlee government came to power in 1945 determined to plan comprehensively. Yet, the aspiration to create a fully planned economy was not met. This book explores the origins and evolution of the promise, in order to explain why it was not fulfilled. RICHARD TOYE lectures in history at Homerton College, Cambridge.