In law, an alien is any person who is not a citizen or a national of a specific country, although definitions and terminology differ to some degree depending upon the continent or region. More generally, however, the term "alien" is perceived as synonymous with foreign national.

Australian nationality law details the conditions by which a person is a national of Australia. The primary law governing nationality regulations is the Australian Citizenship Act 2007, which came into force on 1 July 2007 and is applicable in all states and territories of Australia.