Günther Hans Frei (born 19 May 1942 in St. Gallen) is a Swiss mathematician and historian of mathematics.
Frei studied mathematics, physics and languages at the University of Zurich.
There he received his doctoral degree in 1968 with advisor Bartel Leendert van der Waerden and dissertation on geometry (Beiträge zur axiomatischen Inhaltstheorie).
He became an instructor in 1968 at the University of Notre Dame and in 1970 at Quebec's Université Laval, where he became in 1971 a professor.
He remained there until he retired as professor emeritus and returned to Switzerland to live in Hombrechtikon.