The Lieber Code of April 24, 1863, also known as Instructions for the Government of Armies of the United States in the Field, General Order № 100, or Lieber Instructions, was an instruction signed by President Abraham Lincoln to the Union Forces of the United States during the American Civil War that dictated how soldiers should conduct themselves in wartime. It was named after the German-American jurist and political philosopher Francis Lieber. The main sections were concerned with martial law, military jurisdiction, and the treatment of spies, deserters and prisoners of war.