Citizenship is full membership in a nation or in some other unit of government. Citizenship is also called nationality. Almost all people have citizenship in at least one country. Citizens have certain rights, such as the right to vote and the right to hold public office. They also have certain duties, such as the duty to pay taxes and to serve on a jury.

Not all the people in a nation are citizens of that country. For example, many countries have noncitizen nationals. The word national is often used as another word for citizen. In some cases, however, national means a person who owes loyalty to a country but lacks full membership in it. Noncitizen nationals of the United States include the people of American Samoa, a group of Pacific islands controlled by the United States. The people of American Samoa have the protection of the U.S. government but lack some of the special rights of citizens.

People who are neither citizens nor noncitizen nationals of a country are aliens there. Most aliens are citizens or noncitizen nationals of one country who are traveling or living in another. Many aliens have a permit called a visa allowing them to visit or live where they do not hold citizenship. Illegal aliens are noncitizens living in a country without proper papers.

The laws or beliefs of a country might deny some rights to certain citizens. Such people are sometimes called second-class citizens. Many have a language, race, or religion different from that of the country's largest or most powerful group. For example, the South African government considered blacks second-class citizens for many years. In 1948, it established a policy of rigid racial segregation called apartheid. Under apartheid, blacks and other nonwhites faced official discrimination in education, employment, and other areas. In addition, blacks were not allowed to vote in national elections. In 1991, the government repealed the last of the laws that had formed the legal basis of apartheid. In 1994, the country held its first national elections in which blacks were allowed to vote.

Under the Constitution and other laws, no American may be made a second-class citizen. Citizens receive equal protection of the law, no matter what their race, color, or religion. But some Americans treat certain groups as second-class citizens despite the law.

The word citizen comes from the Latin word civitas, which in ancient times meant membership in a city. Today, citizenship refers mainly to membership in a nation.