His book Painting and Experience in Fifteenth-Century Italy was profoundly influential in the social history of art, and is (2018) widely used as a textbook in college courses.
He spent a year at Pavia University (1955–56), then taught at an international school in St. Gallen in Switzerland (1956–57), and finally went to Munich to hear the art historian Hans Sedlmayr and where he worked with Ludwig Heinrich Heydenreich on the court of Urbino at the Zentralinstitut für Kunstgeschichte.
On his return to London in 1958 he began a long association with the Warburg Institute, initially working in the photographic collection, where he met Kay Simon, whom he married in 1963.
[citation needed] From 1961, he was Assistant Keeper in the Department of Architecture and Sculpture at the Victoria and Albert Museum, returning to the Warburg Institute in 1965 as lecturer in Renaissance Studies.
These were followed by The Limewood Sculptors of Renaissance Germany (1980), Patterns of Intention (1985), Tiepolo and the Pictorial Intelligence (1994, with Svetlana Alpers), Shadows and Enlightenment (1994) and Words for Pictures (2003).