This list of military legions is in chronological order where possible. In modern times, most units using the name "legion" were composed of soldiers from a specific ethnic, national, religious or ideological background, and that background is often specified in the legion's name. Since the Napoleonic Wars, many countries have used the term "legionnaire" to refer to recruits who are neither citizens nor imperial subjects of the government whose military they enter. These governments often, but do not always, group these foreign recruits into specific units that bear the name "legion."
World War I
- Czechoslovak Legions, Czech and Slovak volunteer forces fighting on the Allied Powers side
- French Armenian Legion, part of the French Army; also involved in the Franco-Turkish War of 1918–21
- Georgian Legion (1914–1918), a unit of the German Army recruited from Georgians
- Infantry Regiment of the Academic Legion, formed by volunteer Polish students in 1918, later taken into the regular Polish Army
- Italian Legione Redenta, an Italian military formation that participated in the Siberian Intervention during the Russian Civil War
- Jewish Legion, in the British Army at Gallipoli and Palestine
- Polish Legion in Finland, fighting for the Finns against the Russians
- Polish Legions in World War I, part of the Austro-Hungarian Army
- Puławy Legion, a Polish formation that was part of the Imperial Russian Army
- Legion of Ukrainian Sich Riflemen, a corps of the Austro-Hungarian Army
World War II
Note: Except for the above, all World War II legions fought on the German side.
- Free Arabian Legion, Arab volunteers, notably from Iraq, and North Africa fighting on the German side.
- Armenian or Armenische Legion, name given to the 812th Armenian Battalion of the German Army, made up largely of Armenian Red Army prisoners of war
- Azərbaycan legionu
(Azerbaijan legion), made up largely of Azerbaijani Red Army prisoners of war
- Blue Legion, Spanish volunteers fighting against the Soviet Union on the Eastern Front
- Crna Legija (Black Legion), the name given to the 1st and 5th Croatian Ustaše Brigades
- Croatian Legion
- Croatian Air Force Legion
- Croatian Anti-Aircraft Legion
- Croatian Naval Legion
- Estonian Legion, a unit in the Waffen SS created in 1942, mainly consisting of Estonian soldiers
- Flemish Legion (Dutch: Vlaams Legioen), recruited among Dutch-speaking volunteers from German-occupied Belgium, notably from Flanders.
- Walloon Legion (French: Légion Wallonie), recruited among French-speaking volunteers from German-occupied Belgium.
- Légion française des combattants
(French Legion of Fighters), a pro-Nazi Vichy French unit
- Legion of French Volunteers Against Bolshevism (LVF), pro-Nazi French
- Georgian Legion (1941–1945), a unit of the German army recruited from Georgians
- Indische Legion, also known as the Free India Legion or Tiger Legion, an Indian unit raised in 1941 and attached to the German Army
- Latvian Legion, a formation of the Waffen-SS created in 1943 and consisting primarily of ethnic Latvians
- Legion of St. George, the original name of the British Free Corps
- Ostlegionen (literally "Eastern Legions"), conscripts and volunteers from the occupied eastern territories recruited into the German Army
- La Légion Tricolore, a pro-Nazi French unit which was absorbed into the LVF after six months
- Volga Tatar Legion, one of several units formed by the Wehrmacht out of Soviet prisoners of war according to their ethnicity