40th Regiment, 40th Infantry Regiment or 40th Armoured Regiment may refer to:

Infantry regiments 40th (2nd Somersetshire) Regiment of Foot, a unit of the United Kingdom Army 40th Infantry Regiment, a unit of the United States Army

Armoured regiments 40th Armor Regiment, a unit of the United States Army 40th Cavalry Regiment, a unit of the United States Army 40th (The King's) Royal Tank Regiment, a unit of the United Kingdom Army 40th/41st Royal Tank Regiment, a unit of the United Kingdom Army

Artillery regiments 40th Regiment Royal Artillery, a unit of the United Kingdom Army

Aviation regiments 40th Fighter Aviation Regiment, a unit of the Yugoslav Air Force

Communications regiments 40 (Ulster) Signal Regiment, a unit of the United Kingdom Army

American Civil War regiments 40th Illinois Volunteer Infantry Regiment, a unit of the Union (Northern) Army during the American Civil War 40th Iowa Volunteer Infantry Regiment, a unit of the Union (Northern) Army during the American Civil War 40th Wisconsin Volunteer Infantry Regiment, a unit of the Union (Northern) Army during the American Civil War 40th New York Volunteer Infantry Regiment, a unit of the Union (Northern) Army during the American Civil War

See also 40th Division (disambiguation) 40th Brigade (disambiguation) 40th Battalion (disambiguation) 40th Squadron (disambiguation)