James Sloss Ackerman (born 1919) is a prominent American architectural historian, a major scholar of Michelangelo's architecture, of Palladio and of Italian Renaissance architectural theory.

He was born in San Francisco. At Yale, 1938-41, he came under the influence of Henri Focillon. His graduate work was at the Institute of Fine Arts, New York University (MA 1947, PhD 1952), where he studied with Richard Krautheimer and Erwin Panofsky. His studies were interrupted by his World War II service in the US Army in Italy, which, however, gave him an opportuniuty to increase his on-site understanding of Italian Renaissance architecture, his specialty -- He was assigned to retrieve the archives secured at the Certosa di Pavia. He was a Fellow at the American Academy in Rome (1949-52). He taught at Berkeley and from 1960 at Harvard as Arthur Kingsley Porter Professor of Fine Arts until his retirement in 1990. He was the editor of The Art Bulletin (1956-60) and Annali d'architettura; Ackerman is a member of the American Academy of Arts and Sciences, the American Philosophical Society, and a corresponding member of the British Academy, the Bavarian Academy of Sciences, the Accademia Olimpica, Vicenza, the Ateneo Veneto, the Accademia di San Luca in Rome and the Royal Academy of Uppsala. He gave the Slade Lectures at Cambridge in 1969-70. He has received six honorary doctorates and is a Grand Officer of the Order of Merit of the Italian Republic, an honorary citizen of Padua, and received the Golden Lion Award at the Venice Biennale of 2008. His rigorous method sets architecture in the broader contexts of cultural and intellectual history. He was awarded the Balzan Prize 2001 for achievement in architectural history and urbanism and the Paul Kristeller citation 2001 of the Renaissance Society of America for lifetime achievement.