**Andrei Yuryevich Okounkov** (Russian: Андре́й Ю́рьевич Окунько́в, *Andrej Okun'kov*) (born July 26, 1969) is a Russian mathematician who works on representation theory and its applications to algebraic geometry, mathematical physics, probability theory and special functions. He is currently a professor at Columbia University and the academic supervisor of HSE International Laboratory of Representation Theory and Mathematical Physics. In 2006, he received the Fields Medal "for his contributions to bridging probability, representation theory and algebraic geometry."

He received his doctorate at Moscow State University in 1995 under Alexandre Kirillov and Grigori Olshanski. He has been a professor at Columbia University since 2010. He was previously a professor at Princeton University from 2002 to 2010, an assistant and associate professor at the University of California, Berkeley, and an instructor at the University of Chicago.

He has worked on the representation theory of infinite symmetric groups, the statistics of plane partitions, and the quantum cohomology of the Hilbert scheme of points in the complex plane. Much of his work on Hilbert schemes was joint with Rahul Pandharipande.

Okounkov, along with Pandharipande, Nikita Nekrasov, and Davesh Maulik, has formulated well-known conjectures relating the Gromov–Witten invariants and Donaldson–Thomas invariants of threefolds.

In 2006, at the 25th International Congress of Mathematicians in Madrid, Spain, he received the Fields Medal "for his contributions to bridging probability, representation theory and algebraic geometry." In 2016 he became a fellow of the American Academy of Arts and Sciences.