Nationality is a legal identification of a person in international law, establishing the person as a subject, a national, of a sovereign state. It affords the state jurisdiction over the person and affords the person the protection of the state against other states.

Article 15 of the Universal Declaration of Human Rights states that "Everyone has the right to a nationality", and "No one shall be arbitrarily deprived of his nationality nor denied the right to change his nationality". By international custom and conventions, it is the right of each state to determine who its nationals are. Such determinations are part of nationality law. In some cases, determinations of nationality are also governed by public international law—for example, by treaties on statelessness and the European Convention on Nationality.

The rights and duties of nationals vary from state to state, and are often complemented by citizenship law, in some contexts to the point where citizenship is synonymous with nationality. However, nationality differs technically and legally from citizenship, which is a different legal relationship between a person and a country. The noun "national" can include both citizens and non-citizens. The most common distinguishing feature of citizenship is that citizens have the right to participate in the political life of the state, such as by voting or standing for election. However, in most modern countries all nationals are citizens of the state, and full citizens are always nationals of the state.

In older texts or other languages the word "nationality", rather than "ethnicity", is often used to refer to an ethnic group (a group of people who share a common ethnic identity, language, culture, lineage, history, and so forth). This older meaning of "nationality" is not defined by political borders or passport ownership and includes nations that lack an independent state (such as the Arameans, Scots, Welsh, English, Andalusians, Basques, Catalans, Kurds, Kabyles, Baluchs, Pashtuns, Berbers, Bosniaks, Palestinians, Hmong, Inuit, Copts, Māori, Wakhis, Xhosas and Zulus, among others). Individuals may also be considered nationals of groups with autonomous status that have ceded some power to a larger sovereign state.

Nationality is also employed as a term for national identity, with some cases of identity politics and nationalism conflating the legal nationality as well as ethnicity with a national identity.