Geoffroi Jacques Flach (February 16, 1846 – December 4, 1919) was a French jurist and historian born at Strasbourg, Alsace, of a family known at least as early as the 16th century, when was the first professor of law at University of Strasbourg. Flach's library was purchased by the University of Missouri in 1920 and is preserved at the University of Missouri Libraries.