List of foreign volunteers

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. 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.

During both world wars, American volunteers served on the allied side before the US joined the war. During World War I, there were even a few Americans who volunteered to fly for the Imperial German Flying Corps.

See also Irish military diaspora.