Eileen Edna le Poer Power was born in 1889, the oldest of three daughters of Philip Ernest le Poer Power, stockbroker, and Mabel Grindley Clegg (see also Beryl Power and Rhoda Power at GCPP Power, B and R respectively). Philip Power was convicted of fraud when Eileen was three, at which point he ceased to be part of the lives of Eileen and her sisters, and Mabel Power died when Eileen was fourteen. After the death of their mother the Power sisters were cared for by their maternal grandfather, Benson Clegg, and their mother's three unmarried sisters. After Oxford High School, Eileen Power came up to Girton in 1907 on a Clothworkers' Scholarship to study history. She took a first class in both parts of the Tripos, in spite of the death of her grandfather during the Easter vacation before her finals. Eileen's lifelong friendships with Margery Spring Rice (nee Garrett) and Gwladys [(Mary) Gwladys Jones, who was always known simply as 'M G' within the Girton circle] were formed during her first three years at Girton. She spent the year 1910-11 on a Gilchrist Scholarship studying at the Ecole des Chartes in Paris, during which she began to formulate plans for research in medieval social and economic history, with a particular emphasis on women's history. These had to be revised somewhat in the light of the constraints of the (Charlotte) Shaw Scholarship for research on women's history at the London School of Economics, which she held from 1911 to 1913. During 1913 and 1914, Eileen combined being Director of Studies in History at Girton with some lectures at the LSE, living between Girton and a shared flat in London. The work which she had started on women's religious communities at the LSE began to take clearer shape in Cambridge and was influenced by Alexander Hamilton Thompson and G G Coulton. Between 1915 and 1918 she held the Pfeiffer Fellowship at Girton, the wartime situation opening up the opportunity for Eileen to do most of the mainstream lecturing for the university in economic history, though she found life in Cambridge very tedious by the later stages of the war. She continued to teach in Cambridge until she won the Kahn Travelling Fellowship in 1920. She was the first woman to win the fellowship, which she used to travel to the far east during 1920 and 1921, visiting India, Burma, Java, Japan and China. In Peking she met Reginald Johnston (who was, inter alia, tutor to Pu Yi, the last emperor of China), to whom she became engaged on a subsequent trip in 1929 (she finally brought the engagement to an end in February 1932). Just before setting off on her travels in 1920, Eileen had more or less finished her first book, Medieval English Nunneries, after eight years work: it went to press while she was away and was published in 1922. On her return from her travels in 1921, she left Cambridge again for the LSE, where she was successively Lecturer (1921-4), Reader (1924-31) and Professor (from 1931) of Economic History. She was also a part-time lecturer in economic history at King's College, London from 1921-22. During the 1920s, she taught a research student, Michael Moissey Postan [known as Munia], a Russian émigré, who also acted as her research assistant for a time and whom she eventually married in December 1937, after which they divided their lives between London and a house at 2 Sylvester Road in Cambridge. She collaborated closely for many years at the LSE with R H Tawney: they jointly founded the Economic History Society in 1926. In the spring of 1930, she spent a term teaching at Barnard College in New York and Vassar College, also giving guest lectures at most of the other seven sister colleges. Her return to London was followed by an offer of a chair at Barnard, but she turned this down in favour of continuing her London life and work. In addition to her academic work, Eileen Power was also an active suffragist, undertaking work for the National Union of Women's Suffrage Societies and lecturing for the League of Nations Union. She also gave lectures for the WEA [Workers' Educational Association]. Eileen Power brought medieval history into general culture in the interwar years: her most famous book, Medieval People, went into ten editions and was still in print decades after it was first published; she wrote history books for children and schools; she wrote frequent reviews; she was a part of literary London, publishing often in the weeklies; and she was a pioneer radio broadcaster. All this was achieved at a relatively young age: Eileen Power died suddenly of a heart attack in August 1940 at the age of 51.