21 Squadron or 21st Squadron may refer to:
- No. 21 Squadron RAAF, Royal Australian Air Force
- No. 21 Squadron (Finland), Finnish Air Force
- 21 Squadron SAAF, South African Air Force
- No. 21 Squadron RAF, United Kingdom Royal Air Force
- 21st Aeromedical Evacuation Squadron, United States Air Force
- 21st Airlift Squadron, United States Air Force
- 21st Bombardment Squadron, United States Air Force
- 21st Fighter Squadron, United States Air Force
- 21st Operational Weather Squadron, United States Air Force
- 21st Photographic Reconnaissance Squadron, United States Air Force
- 21st Pursuit Squadron, United States Army Air Force
- 21st Space Operations Squadron, United States Air Force
- 21st Special Operations Squadron, United States Air Force
- 21st Tactical Air Support Squadron, United States Air Force
See also