Warren John Ewens AO FRS FAA (born 23 January 1937 in Canberra) is an Australian-born mathematician who has been Professor of Biology at the University of Pennsylvania since 1997. (He also held that position 1972–1977.) He concentrates his research on the mathematical, statistical and theoretical aspects of population genetics. Ewens has worked in mathematical population genetics, computational biology, and evolutionary population genetics. He introduced Ewens's sampling formula. Since 2006, he has taught statistics at the University of Pennsylvania's Wharton School.