Multiple citizenship is a status in which a person is concurrently regarded as a citizen under the laws of more than one state. Multiple citizenships exist because different countries use different, and not necessarily mutually exclusive, citizenship requirements. Colloquial speech refers to people "holding" multiple citizenship but technically each nation makes a claim that this person be considered its national. For this reason, it is possible for a person to be a citizen of one or more countries, or even no country.
Individual countries follow their own rationales in establishing their criteria for citizenship. Each country has different requirements and policies on both acquiring its citizenship and holding other citizenships concurrently. These laws sometimes create situations where someone may acquire other citizenships without rendering the original citizenship invalid, or where someone may satisfy the citizenship requirements of more than one country simultaneously through no action of his or her own (e.g. at birth). This would allow the individual to hold two or more nationalities. Here are common reasons to bestow citizenship:
Once a country bestows citizenship, it may or may not consider a voluntary renunciation of that citizenship to be valid. In the case of naturalization, some countries require applicants for naturalization to renounce their former citizenship. However, this renunciation may not be recognized by the renounced country. Technically, the person in question may still possess both citizenships.
For example, United States Chief Justice John Rutledge ruled "a man may, at the same time, enjoy the rights of citizenship under two governments," but the US requires applicants for naturalization to swear to an oath renouncing all prior "allegiance and fidelity" to any other nation or sovereignty as part of the naturalization ceremony. In the case of a British citizen, however, the UK honors renunciation of citizenship only if done with competent UK authorities. Consequently, British citizens naturalized in the US remain British citizens in the eyes of the British government even after they renounce British allegiance to the satisfaction of U.S. authorities.