For other uses see Allies (disambiguation).
In general, allies are people, groups or nations that have joined together in an association for mutual benefit or to achieve some common purpose. In English usage, those who share a common goal and whose work toward that goal is complementary may be viewed as allies for various purposes even when no explicit agreement has been worked out between them. Similarly, when the term is used in the context of war or armed struggle, a formal military alliance is not required for being perceived as an ally—co-belligerence, to fight alongside someone, is enough. According to this general usage, allies become allies not when concluding an alliance treaty but when struck by war.
"Allies" spelled with a capital "A", usually denotes the countries who fought together against the Central Powers in World War I, (the Allies of World War I) or those who fought against the Axis Powers in World War II (the Allies of World War II).
The Allied Nations has been a name for a few organisations and factions in popular media, such as the Mercenaries games. The Allies in the series include the nations of the World War II alliance plus Germany, allied in the face of Soviet aggression towards Europe.