Nationality is a legal relationship existing between a person and a state. The person becomes subject to the state's jurisdiction, even while not on the state's territory; in exchange the subject becomes entitled to the state's protection, and to other rights as well.
Nationality must be distinguished from citizenship: citizens have rights to pariticipate in the politicial life of the state they are a citizen of, such as by voting or standing for election; while nationals need not have these rights, though normally they do.
The nationals of a state generally possess the right of abode in the territory of the state they are nationals of, though there are some exceptions (e.g. the United Kingdom).
Traditionally under international law, determining who its nationals are was the exclusive competence of the state in question. However there were nonetheless many similarities in the laws of each nation, and today the law of nationality is increasingly coming under regulation, e.g. by the various conventions on statelessness, and the European Convention of Nationality.
A person who is not a national of any state is referred to a stateless person.
The nationality of a legal person (e.g. a corporation) is generally the state under whose laws the legal person is registered.
See nationalism. (The nationality entry needs to be better integrated with the nationalism entry.)