James Phinney Baxter III (February 15, 1893 – June 17, 1975) was an American historian, educator and academic. He won the 1947 Pulitzer Prize for history, for his book Scientists Against Time. He was also the author of The Introduction of the Ironclad Warship, which he wrote in 1933.
Baxter taught at Colorado College and then at Harvard, progressing from Instructor to full Professor in 10 years. He served as Master of Adams House. He was elected a Fellow of the American Academy of Arts and Sciences in 1928. In 1937, he became president of Williams College.
In 1943 he was the part-time official historian of the Office of Scientific Research and Development, while serving as president of Williams College from 1937-1961. He was a member of the board of trustees of the World Peace Foundation.