thumb|Hans Christoph Ernst von Gagern.
Hans Christoph Ernst Freiherr von Gagern (25 January 176622 October 1852), German statesman and political writer, was born at Kleinniedesheim, near Worms. After studying law at the universities of Leipzig and Göttingen, he entered the service of the Prince of Nassau-Weilburg, whom in 1791 he represented at the imperial diet.
He was afterwards appointed the prince's envoy at Paris, where he remained until the decree of Napoleon, forbidding all persons born on the left side of the Rhine to serve any other state than France, compelled him to resign his office (1811).