A partisan is a member of an irregular military force formed to oppose control of an area by a foreign power or by an army of occupation by some kind of insurgent activity.

The Partisan Ranger Act was passed on April 21, 1862, by the Confederate Congress. It was intended as a stimulus for recruitment of irregulars for service into the Confederate Army during the American Civil War. The Confederate leadership, like the Union leadership, later opposed the use of unconventional warfare out of fear the lack of discipline among rival guerrilla groups could spiral out of control. On February 17, 1864, the law was repealed after pressure from General Robert E. Lee and other Confederate regulars.