Hans Hahn (1879 - 1934) was an Austrian mathematician who made many contributions to functional analysis, topology, set theory, the calculus of variations, real analysis, and order theory. He was also actively interested in philosophy, being a member of the Vienna Circle.

Hahn's contributions to mathematics include the famous Hahn-Banach theorem and (independently of Banach and Steinhaus) the uniform boundedness principle. Other theorems are the Hahn decomposition theorem, the Vitali-Hahn-Saks theorem, the Hahn-Mazurkiewicz theorem and the Hahn embedding theorem.