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.
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. British Nationality Law).
Nationality must be distinguished from citizenship: 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; while nationals need not have these rights, though normally they do.
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 on Nationality.