John Monroe Van Vleck (March 4, 1833–November 4, 1912) was an American mathematician and astronomer. He taught astronomy and mathematics at Wesleyan University in Middletown, Connecticut for more than 50 years (1853-1912) and served as acting university president twice. The Van Vleck Observatory (at Wesleyan University) and the crater Van Vleck on the Moon are named after him.