Paul Oskar Kristeller studied the thought and philosophy of late antiquity, the Middle Ages, and the Renaissance.
He devoted much of his career to identifying medieval and Renaissance manuscripts as sources for the history of thought, and edited or studied some of them in detail. The manuscripts, many of them uncatalogued or inadequately described, are found in libraries throughout the world. The results of this project are published in six volumes under the title, Iter Italicum. Kristeller also published works dealing with the histories of Platonism, Aristotelianism, stoicism, humanism, medicine and the sciences, theology and rhetoric, the theory of the arts, literature and music, and education.
From 1939 to 1973, Kristeller taught at Columbia University, where he was the Frederick J. E. Woodbridge Professor Emeritus of Philosophy. He was a fellow of the American Academy of Arts and Sciences, the Medieval Academy of America, and the American Philosophical Society, and an honorary fellow of the Pierpont Morgan Library. He was the recipient of numerous awards, including Guggenheim Fellowships (1958, 1968) and the first Newberry Library Award for contribution to the humanities (1987).
Kristeller received a Ph.D. (1928) from the University of Heidelberg, and a second Ph.D. (1937) from the University of Pisa.