Renunciation of citizenship is the voluntary loss of citizenship. It is the opposite of naturalization, whereby a person voluntarily obtains citizenship. It is distinct from denaturalization, where citizenship is revoked by the state.

The common law doctrine of perpetual allegiance denied an individual the right to renounce obligations to his sovereign. The bonds of subjecthood were conceived in principle to be both singular and immutable. These practices held on in varying ways until the late 19th century.

The refusal of many states to recognize expatriation became problematic for the United States, which had a large immigrant population. The War of 1812 was caused partly by Britain's impressment of US citizens born in the UK into the Royal Navy. Immigrants to the US were sometimes held to the obligations of their foreign citizenship when they visited their home countries. In response, the US government passed the Expatriation Act of 1868 and concluded various treaties, the Bancroft Treaties, recognizing the right to renounce one's citizenship.

During World War II, over 120,000 Japanese Americans were placed in internment camps throughout the West Coast of the United States. Conditions in the camps were often sub-par, with cruel emotional and sometimes physical mistreatment. This, along with a "loyalty questionnaire" that required the Japanese to renounce any loyalty to the Japanese Emperor, led a total of 5,589 Japanese American Nisei to renounce their American citizenship.

"My renunciation had been an expression of momentary emotional defiance in reaction to years of persecution suffered by myself and other Japanese Americans"

— Minoru Kiyota

Renunciation of citizenship is particularly relevant in cases of multiple citizenship, given that additional citizenships may be acquired automatically and may be undesirable. Many countries have pragmatic policies that recognize the often arbitrary nature of citizenship claims of other countries and negative consequences, such as loss of security clearance, can mostly be expected only for actively exercising foreign citizenship, for instance by obtaining a foreign passport. People from some countries renounce their citizenship to avoid compulsory military service. However, some people may wish to be free even of the purely theoretical obligations and appearance of dual loyalty that another citizenship implies. Even in countries that allow dual citizenship, such as Australia, Jamaica and Pakistan, electoral laws demand that politicians not be under an obligation of allegiance to any foreign country, and so when politicians have been found to be violating such laws, they stepped down and renounced their other citizenships in response to the public controversy. Another example may be political refugees who would wish to renounce allegiance to the country from which they escaped.

Each country sets its own policies for formal renunciation of citizenship. There is a common concern that individuals about to relinquish their citizenship do not become a stateless person, and many countries require evidence of another citizenship or an official promise to grant citizenship before they release that person from citizenship. Some countries may not allow or do not recognize renunciation of citizenship or establish administrative procedures that are essentially impossible to complete.