Paul Monsky (born June 17, 1936) is an American mathematician and professor at Brandeis University.
After earning a bachelor's degree from Swarthmore College, he received his Ph. D. in 1962 from the University of Chicago under the supervision of Walter Bailey. He has introduced the Monsky-Washnitzer cohomology and he has worked intensively on Hilbert–Kunz functions and Hilbert–Kunz multiplicity. In 2007, Monsky and Brenner gave an example showing that tight closure does not commute with localization.
Monsky's theorem, the statement that a square cannot be divided into an odd number of equal-area triangles, is named after Monsky, who published the first proof of it in 1970.
In the mid-1970s, Monsky stopped paying U.S. federal income tax in protest against military spending. He resisted income tax withholding by claiming extra exemptions, and this led to a criminal conviction on tax charges in 1980.