20th Regiment
- 20th Arkansas Infantry Regiment
- 20th Connecticut Infantry Regiment
- 20th Continental Regiment
- 20th Duke of Cambridge's Own Infantry (Brownlow's Punjabis)
- 20th Field Artillery Regiment (United States)
- 20th Field Artillery Regiment, RCA
- 20th Hussars
- 20th Illinois Infantry Regiment
- 20th Indiana Infantry Regiment
- 20th Infantry Regiment (United States)
- 20th Iowa Infantry Regiment
- 20th Kansas Militia Infantry Regiment
- 20th Kentucky Infantry Regiment
- 20th Lancers (Pakistan)
- 20th Light Dragoons
- 20th Maine Infantry Regiment
- 20th Marine Regiment (United States)
- 20th Massachusetts Infantry Regiment
- 20th Michigan Infantry Regiment
- 20th New York Infantry Regiment
- 20th Pennsylvania Infantry Regiment
- 20th Regiment of Bengal Native Infantry
- 20th Regiment of Foot
- 20th Surveillance and Target Acquisition Regiment, Royal Australian Artillery
- 20th Tennessee Infantry Regiment
- 20th Virginia Infantry Regiment
- 20th Wisconsin Infantry Regiment