Francis Lieber (born Franz Lieber; 18 March 1798 – 2 October 1872) was a German and American jurist and political philosopher. He is best known for the Lieber Code, the first modern codification of the customary law and the laws of war for battlefield conduct, which served as a basis for the Hague Conventions of 1899 and 1907 and for the later Geneva Conventions. He was also a pioneer in the fields of law, political science, and sociology in the United States.
Born in Berlin, Prussia, to a Jewish merchant family, Lieber served in the Prussian Army during the Wars of Liberation against Napoleon Bonaparte. He obtained a doctorate from the University of Jena in 1820. A republican, he volunteered to fight on the Greek side in the Greek War of Independence in 1821. After experiencing repression in Prussia for his political views, he emigrated to the United States in 1827. During his early years in America, he worked a number of jobs, including swimming and gymnastics instructor, editor of the first editions of the Encyclopaedia Americana, journalist, and translator.