Henry Frederick "Fritz" Schaefer III (born June 8, 1944) is a computational and theoretical chemist. He is one of the most highly cited chemists in the world, with a Thomson Reuters H-Index of 121 as of 2020.

Schaefer is a fellow of the American Academy of Arts and Sciences, American Physical Society, American Association for the Advancement of Science, Royal Society of Chemistry, American Chemical Society, and an honorary fellow of the Chemical Research Society of India, among others. Schaefer is an outspoken Christian. He has described himself as sympathetic to teleological arguments, but primarily a "proponent of Jesus."