Leo Anthony Harrington (born May 17, 1946) is a professor of mathematics at the University of California, Berkeley who works in recursion theory, model theory, and set theory. Having retired from being a Mathematician, Professor Leo Harrington is now a Philosopher. His notable results include proving the Paris–Harrington theorem along with Jeff Paris, showing that if the axiom of determinacy holds for all analytic sets then x# exists for all reals x, and proving with Saharon Shelah that the first-order theory of the partially ordered set of recursively enumerable Turing degrees is undecidable.