See P. Weis, Nationality and Statelessness in International Law (1956); B. Akzin, States and Nations (1966); C. Joseph, Nationality and Diplomatic Protection (1969).
Nationality is a relationship between a person and their state of origin, culture, association, affiliation and/or loyalty. Nationality affords the state jurisdiction over the person, and affords the person the protection of the state.
Traditionally under international law and conflict of laws principles, it is the right of each state to determine who its nationals are. Today the law of nationality is increasingly coming under more international regulation by various conventions on statelessness, as well as some multilateral treaties such as the European Convention on Nationality.
The legal sense of nationality, particularly in the English speaking world, may often mean citizenship, although they do not mean the same thing everywhere in the world; for instance, in the UK, citizenship is a branch of nationality which in turn ramifies to include other subcategories (see British nationality law). Citizens have rights to participate in the political life of the state of which they are a citizen, such as by voting or standing for election. Nationals need not immediately have these rights; they may often acquire them in due time.
Nationality can also mean membership in a cultural/historical group related to political or national identity, even if it currently lacks a formal state. This meaning is said by some authorities to cover many groups, including Kurds, Basques, Catalans, English, Welsh, Scots, Venetians,Palestinians, Tamils, Quebecers and many others.
The person remains subject to the state's jurisdiction (the lex domicilii in Conflict of Laws) for the purposes of defining status and capacity wherever he or she might travel outside the state's territory; in exchange, the individual is entitled to the state's protection, and to other rights as well. This is an aspect of the public policy of parens patriae and derives from the social contract. In the civil law systems of continental Europe, either the law of nationality (known as the lex patriae) or the law of the place of habitual residence is preferred to domicile as the test of a person's status and capacity.
Some countries do not permit dual nationality while others only allow a very limited form of dual citizenship (e.g. Indian nationality law, South African nationality law, Republic of China nationality law). A person who is not a national of any state is declared a stateless person.
In the United States, the term "national" usually means someone who has U.S. nationality, but not United States citizenship, by virtue of living in a U.S. territory. Though it applied to other U.S. territories in the past, today only residents of American Samoa and Swains Island are considered U.S. "nationals"; Congress has granted full citizenship to residents of the remaining territories. U.S. "nationals" have the same rights to enter, live, and work in the United States as citizens; voting rights are the only major difference. Legally, however (and in the broader sense), U.S. citizens are also U.S. nationals; United States passports do not distinguish between citizens and non-citizen nationals.