First Army may refer to:
China New 1st Army, Republic of China First Field Army, a Chinese Communist Party unit in the Chinese Civil War 1st Group Army, People's Republic of China
Germany 1st Army (German Empire), a World War I field Army 1st Army (Wehrmacht), a World War II field army 1st Panzer Army 1st Parachute Army (Wehrmacht)
Russia and the Soviet Union First Western Army 1st Army (Russian Empire) 1st Red Banner Army 1st Shock Army 1st Guards Tank Army (Russia)
Others First Allied Airborne Army First Australian Army 1st Army (Austria-Hungary) First Army (United Kingdom) First Army (Bulgaria) First Canadian Army 1st Army (France) First Army (Greece) First Army (Hungary) First Army (Italy) First Army (Japan) First Army (Ottoman Empire) First Polish Army (1920) First Polish Army (1944–1945) First Army (Romania) First Army (Serbia) First Army (Turkey) First Army (United Arab Republic) First United States Army 1st Army (Kingdom of Yugoslavia) 1st Army (Yugoslav Partisans)
See also I Corps (disambiguation) 1st Division (disambiguation) 1st Brigade (disambiguation) 1st Regiment (disambiguation)