Warm thanks to my literary agents Cara Jones of Rogers, Coleridge and White, London, and Melanie Jackson of Melanie Jackson Agency, New York; also to my editors Juliet Annan of Fig Tree Penguin, London, and Ginny Smith of Penguin Press, New York, and to copy-editor Sarah Day. I benefited greatly from visits to museums and galleries including the Centre Pompidou and the Orangerie in Paris, the Tate Modern, the Royal Academy of Arts and the Saatchi Gallery in London and the Whitney Museum in New York. In researching the pictures, I was grateful for the assistance of John Moelwyn-Hughes and Siân Phillips of Bridgeman Art Library and of Elizabeth Walley of DACS. Steve Ward has generously supported and encouraged me throughout. My post as Royal Literary Fund Fellow at the University of Sussex contributed substantially to the completion of the research.