He was curator and then senior curator in the Department of Painting and Sculpture at the Museum of Modern Art, New York, from 1990 to 2002, where he organized thematic exhibitions such as "Dislocations" and "Modern Art Despite Modernism" as well as monographic shows on Elizabeth Murray, Gerhard Richter, Max Beckmann, Tony Smith and Robert Ryman. In addition he coordinated the Projects series from 1990 to 2000. In 2002, and in that context, he mounted exhibitions with Art Spiegelman, Ann Hamilton and Franz West among others.

From 2005 to 2007 he was visual arts Director of the Venice Biennale, the first American invited to assume that position.

He has been a contributing editor at Art in America since 1981 and writes frequently for Artforum, Parkett, Art Press (Paris), Frieze (London) and Corriere della Sera (Milan). He has also written numerous catalogs, articles, and books including Philip Guston (Abbeville, 1986), Cate: 6 Paintings by Gerhard Richter (2009) Chuck Close (with Lisa Lyons, Rizzoli, 1987), and the forthcoming Intimate Geometries: The Work and Life of Louise Bourgeois. Among his many honors he has received a Penny McCall Foundation Grant for painting, a Norton Family Foundation Curator Grant, and honorary doctorates from the School of the Art Institute of Chicago, the Maine College of Art as well as awards from the American Chapter of the International Association of Arts Critics, a special AICA award for Distinguished Contribution to the Field of Art Criticism, an ICI Agnes Gund Curatorial Award, and the Lawrence A. Fleischman Award for Scholarly Excellence in the Field of American Art History from the Smithsonian Institution's Archives of American Art. In 2000 the French Ministry of Culture presented him with the medal of Chevalier des Arts et des Lettres and subsequently awarded him the status of "Officer" in the same order.