This is the first biography of Lionel Curtis, a highly influential figure in international affairs throughout the first half of the twentieth century. He was instrumental in extending self-government to the 'new South Africa' in 1910, India in 1916, and Eire after 1921. He worked to associate the Commonwealth with America in 1918 and towards a united Europe in 1948. He was founder of the Round Table, the Royal Institute of International Affairs, and the Oxford Society.