Dennis Arnold Hejhal (born December 10, 1948, in Chicago) is an American mathematician.
In 1967, as a college freshman, Hejhal scored among the top 5 in the U.S. in the William Lowell Putnam Mathematical Competition.
He was a guest professor at Princeton University in 1993 and at the Institute for Advanced Study on several occasions since 1983.
Hejhal works on analytic number theory, automorphic forms, the Selberg trace formula and quantum chaos.
In 1986 he was an invited speaker at the International Congress of Mathematicians in Berkeley (Zeros of Epstein Zeta Functions and Supercomputers).