Paul Althaus Smith (1900 – June 13, 1980) was an American mathematician. His name occurs in two significant conjectures in geometric topology: the Smith conjecture, which is now a theorem, and the Hilbert–Smith conjecture, still open as of 2010[update]. Smith theory is a theory about homeomorphisms of finite order of manifolds, particularly spheres.
Smith was a student of Solomon Lefschetz at the University of Kansas, moving to Princeton University with Lefschetz in the mid-1920s. He finished his doctorate at Princeton, in 1926. His PhD thesis was published in the Annals of Mathematics that same year. He also worked with George David Birkhoff, with whom he wrote a 1928 paper in ergodic theory, entitled Structure analysis of surface transformations, which appeared in the Journal des Mathématiques.
He subsequently became a professor at Columbia University and at the Barnard College.
Smith was married to a Swiss–American early music pioneer Suzanne Bloch.