Nationality is a legal relationship between an individual person and a state.^[12] Nationality affords the state jurisdiction over the person and affords the person the protection of the state. What these rights and duties are varies from state to state.^[13]

By custom and international conventions, it is the right of each state to determine who its nationals are.^[14] 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.

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.^[12][15]

In older texts, the word nationality rather than ethnicity, 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, Basques, Catalans, Kurds, Kabyles, Baloch, Berbers, Bosniaks, Kashmiris, Palestinians, Sindhi, Tamils, Hmong, Inuit, Copts, Māori, Sikhs, Wakhi, Székelys, Xhosas and Zulus).

Individuals may also be considered nationals of groups with autonomous status that have ceded some power to a larger government.

Nationality is the status that allows a nation to grant rights to the subject and to impose obligations upon the subject.^[15] In most cases, no rights or obligations are automatically attached to this status, although the status is a necessary precondition for any rights and obligations created by the state.^[16]

In European law, nationality is the status or relationship that gives a nation the right to protect a person from other nations.^[15] Diplomatic and consular protection are dependent upon this relationship between the person and the state.^[15] A person's status as being the national of a country is used to resolve the conflict of laws.^[16]

Within the broad limits imposed by few treaties and international law, states may freely define who are and are not their nationals.^[15] However, since the Nottebohm case, other states are only required to respect claim by a state to protect an alleged national if the nationality is based on a true social bond.^[15] In the case of dual nationality, states may determine the most effective nationality for a person, to determine which state's laws are most relevant.^[16] There are also limits on removing a person's status as a national. 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."

Nationals normally have the right to enter or return to the country they belong to. Passports are issued to nationals of a state, rather than only to citizens, because the passport is the travel document used to enter the country. However, nationals may not have the right of abode (the right to live permanently) in the countries that grant them passports.

Conceptually, citizenship is focused on the internal political life of the state and nationality is a matter of international dealings.^[17]

In the modern era, the concept of full citizenship encompasses not only active political rights, but full civil rights and social rights.^[15] Nationality is a necessary but not sufficient condition to exercise full political rights within a state or other polity.^[12] Nationality is required for full citizenship, and some people have no nationality in international law. A person who is denied full citizenship or nationality is commonly called a stateless person.

Historically, the most significant difference between a national and a citizen is that the citizen has the right to vote for elected officials, and to be elected.^[15] This distinction between full citizenship and other, lesser relationships goes back to antiquity.

Until the 19th and 20th centuries, it was typical for only a small percentage of people who belonged to a city or state to be full citizens.

In the past, most people were excluded from citizenship on the basis of sex, socioeconomic class, ethnicity, religion, and other factors.

However, they held a legal relationship with their government akin to the modern concept of nationality.^[15]

United States nationality law defines some persons born in U.S. outlying possessions as U.S. nationals but not citizens. British nationality law defines six classes of British national, among which "British citizen" is one class (having the right of abode in the United Kingdom, along with some "British subjects"). Similarly, in the Republic of China, commonly known as Taiwan, the status of national without household registration applies to people who have Republic of China nationality, but do not have an automatic entitlement to enter or reside in the Taiwan Area, and do not qualify for civic rights and duties there. Under the nationality laws of Mexico, Colombia, and some other Latin American countries, nationals do not become citizens until they turn 18.

Nationality is sometimes used simply as an alternative word for ethnicity or national origin, just as some people assume that citizenship and nationality are identical.^[18] cognate]] word for understood as a synonym of ethnicity or as an identifier of cultural and family-based self-determination, rather than on relations with a state or current government. For example, some Kurds say that they have Kurdish nationality, even though there is no Kurdish sovereign state at this time in history.

In the context of former Soviet Union and former Socialist Federal Republic of Yugoslavia, "nationality" is often used as translation of the Russian nacional'nost' and Serbo-Croatian narodnost, which were the terms used in those countries for ethnic groups and local affiliations within the member states of the federation. In the Soviet Union, more than 100 such groups were formally recognized. Membership in these groups was identified on Soviet internal passports, and recorded in censuses in both the USSR and Yugoslavia. In the early years of the Soviet Union's existence, ethnicity was usually determined by the person's native language, and sometimes through religion or cultural factors, such as clothing.^[19] Children born after the revolution were categorized according to their parents' recorded ethnicities. Many of these ethnic groups are still recognized by modern Russia and other countries.

Similarly, the term nationalities of China refers to ethnic and cultural groups in China. Spain is one nation, made up of nationalities, which are not politically recognized as nations (state), but can be considered smaller nations within the Spanish nation. Spanish law recognises the autonomous communities of Andalusia, Aragon, Balearic Islands, Canary Islands, Catalonia, Valencia, Galicia and the Basque Country as "nationalities" (nacionalidades).

National identity is a person's subjective sense of belonging to one state or to one nation. A person may be a national of a state, in the sense of being its citizen, without subjectively or emotionally feeling a part of that state, for example many migrants in Europe often identify with their ancestral and/or religious background rather than with the state of which they are citizens. Conversely, a person may feel that he belongs to one state without having any legal relationship to it. For example, children who were brought to the U.S. illegally when quite young and grow up there with little contact with their native country and its culture often have a national identity of feeling American, despite legally being nationals of a different country.

Dual nationality is when a single person has a formal relationship with two separate, sovereign states.^[17] This might occur, for example, if a person's parents are nationals of separate countries, and the mother's country claims all offspring of the mother's as their own nationals, but the father's country claims all offspring of the father's.

Nationality, with its historical origins in allegiance to a sovereign monarch, was seen originally as a permanent, inherent, unchangeable condition, and later, when a change of allegiance was permitted, as a strictly exclusive relationship, so that becoming a national of one state required rejecting the previous state.^[17]

Dual nationality was considered a problem that caused conflict between states and sometimes imposed mutually exclusive requirements on affected people, such as simultaneously serving in two countries' military forces.

Through the middle of the 20th century, many international agreements were focused on reducing the possibility of dual nationality.

Since then, many accords recognizing and regulating dual nationality have been formed.^[17]

Statelessness is the condition in which an individual has no formal or protective relationship with any state. This might occur, for example, if a person's parents are nationals of separate countries, and the mother's country rejects all offspring of mothers married to foreign fathers, but the father's country rejects all offspring born to foreign mothers. Although this person may have an emotional national identity, he or she may not legally be the national of any state.

Another stateless situation arises when a person holds a travel document (passport) which recognizes the bearer as having the nationality of a "state" which is not internationally recognized, has no entry in the International Organization for Standardization's country list, is not a member of the United Nations, etc. In the current era, persons native to Taiwan who hold Republic of China passports are one example.

^{[21] [22]}

The following list includes states in which parents are able to confer nationality on their children or spouses.^[23][24]