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

Military

Recent

• 501st Aviation Regiment - A unit of the United States 1st Armored Division
• 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 villan costumes from the Star Wars universe
• 501st Legion Southern Outpost - A part of the 501st Legion Star Wars costuming club.