Lewis Namier was one of the most important historians of the twentieth century. His work on the politics of the 1760s, based on the ‘scientific’ analysis of a mass of contemporary documents, and emphasising the material and psychological elements of human motivation, was seen by contemporaries as ’revolutionary’ and remains controversial. It gave a new word to the English language: to Namierise. Moreover, Namier played a major role in public affairs, in the Foreign Office, 1915–20, and in the Zionist Organisation in the 1930s, and was close to many of the leading figures of his day. This is the first biography of Namier for half a century, and the first to integrate all aspects of his life and thought. Based on a comprehensive range of sources, including the entire corpus of Namier’s writings, it provides a full account of his background, examines his role in politics and reconstructs his work as a historian, showing the origins and development of his ideas about the past, and the subjects which preoccupied him: nationalism, empire, and the psychology of individuals and groups. Namier’s life and writings illuminate many of the key events of the twentieth century, his belief in the power of nationalism and the importance of national territory, foreshadowing problems which still beset our own world.