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.
John Monroe Van Vleck was born on March 4, 1833, in Stone Ridge, New York; he was the son of Peter Van Vleck (1806-1872) and Ann Hasbrouck (1803-1854). His maternal grandparents were Joseph Hasbrouck (1754-1831) and Margaret Hoornbeck Hasbrouck (1768-1831). He graduated from Wesleyan University in 1850, and began teaching at Greenwich Academy. The degree of LL.D. was conferred on him by Northwestern University in 1876. From 1851-53 he had been an assistant at the Nautical Almanac Office.
He taught astronomy and mathematics at Wesleyan University in Middletown, Connecticut for more than 50 years, serving as adjunct professor of Mathematics 1853-57, professor of Mathematics and Astronomy 1858-1904, and professor emeritus 1904-12. He served as the acting president for the university on two occasions, 1872–73 and 1887–89, the vice president 1890-93. In 1904 he was vice-president of the American Mathematical Society.
He was a member of the Connecticut Academy of Arts and Sciences.
In 1869 he was a member of the Solar Eclipse Expedition to Mount Pleasant, Iowa. He was a fellow of the A.A.A.S. His publications include "Tables giving the Positions of the Moon for 1855-'6" and for 1878-91, and similar "Tables giving the Positions of Saturn for 1857 to 1877" contributed to the "American Nautical Almanac".