This article is about foreign volunteers who are serving in forces of a country other than their own, but who are not primarily motivated by personal financial gain. For soldiers recruited in colonies, see Colonial troops. For soldiers in foreign armies who are motivated by personal financial gain, see Mercenaries. For foreign soldiers temporarily serving in another country's military, see Exchange officer.
The armed forces of many nations have, at one time or another, used foreign volunteers who are motivated by political, ideological or other considerations to join a foreign army.[1] These may be formed into units of a given nationality or may be formed into mixed nationality foreign units. Sometimes foreign volunteers were or are incorporated into ordinary units. The practice has a long history, dating back at least as far as the Roman Empire, which recruited non-citizens into Auxiliary units on the promise of them receiving Roman citizenship for themselves and their descendants at the end of their service.[2]