Michael H. Hart (born April 27, 1932) is an American astrophysicist and author, known for his work both in astrophysics and in writing on controversial historical and sociopolitical subjects. He is the author of the best-selling book, The 100: A Ranking of the Most Influential Persons in History.

Hart was born in New York City and graduated from the Bronx High School of Science. He served in the U.S. Army during the Korean War. He received his undergraduate degree in mathematics from Cornell University and later earned a Ph.D. in astrophysics from Princeton University. Hart also holds graduate degrees in physics, astronomy, and computer science, as well as a law degree. He worked as a research scientist at NASA before becoming a professor of physics at Trinity University in San Antonio.

Michael H. Hart describes himself as a Jeffersonian liberal, although his critics view him as a conservative and racial separatist.