This article reviews the rich internationalist literature produced by a group of Cambridge Apostles in the interwar years, and evaluates it in the context of contemporary British idealist thought. John Maynard Keynes, Bertrand Russell, Ralph Hawtrey, Leonard Woolf, Gerald Shove, Hugh Meredith, Goldsworthy Lowes Dickinson, Julian Bell, Dennis Robertson and Hugh Dalton not only wrote extensively on international relations, but were widely read and politically influential. Although they never constituted a formal advocacy group or organization, their views on the First World War, the League of Nations, the British Empire and international trade were significantly similar. They also unanimously opposed conscription when it was introduced in Britain in 1916. Their approach appears original especially as far as its ethical foundation, based on Moore’s Principia Ethica, is concerned. The central role played by economic arguments in their reflections is also pointed out.