501st

501st may refer to:

Fiction

 * 501st Legion (Star Wars) - A fictional legion within the Star Wars expanded universe
 * 501st Joint Fighter Wing - A fictional air force unit in the anime series Strike Witches

Recent

 * 501st Combat Support Wing
 * 501st Infantry Regiment (United States)
 * 501st Military Intelligence Battalion (United States)
 * 501st Military Intelligence Brigade (United States)
 * 501st Sustainment Brigade (United States)

Historical

 * 501st Aircraft Control and Warning Battalion - A forerunner of the 603rd Air Control Squadron
 * 501st Reconnaissance Battalion - A former unit of the United States 15th Cavalry Regiment
 * 501st Bombardment Group - A forerunner of the 501st Combat Support Wing
 * 501st Tactical Missile Wing - A former unit of the United States Third Air Force
 * 501st heavy tank battalion (Germany)

Other

 * 501st Legion - A fan-based organization dedicated to screen-accurate replicas of villain costumes from the Star Wars universe