Citizenship of the United States
A person who is considered a citizen by more than one nation has "dual citizenship". It is possible for a United States citizen to have dual citizenship; this can be achieved in various ways, such as by birth in the United States to a parent who is a citizen of a foreign country (or in certain circumstances the foreign nationality may be transmitted even by a grandparent) by birth in another country to a parent(s) who is/are a United States citizen/s, or by having parents who are citizens of different countries. Anyone who becomes a naturalized U.S. citizen is required to renounce any prior "allegiance" to other countries during the naturalization ceremony; however, this renunciation of allegiance renunciation of citizenship to those countries.
Relinquishment of United States nationality
Even countries which permit dual citizenship may bar dual citizens from government positions. Australia for example does not allow dual citizens to stand for election to Parliament, while Taiwan bars dual citizens from most public-sector positions. Diplomatic and consular positions present additional difficulties. The Vienna Convention on Diplomatic Relations and Vienna Convention on Consular Relations state that a country may refuse to receive a diplomat or consular officer who holds the citizenship of the receiving country. Based on this, the State Department does not receive U.S. citizens and non-citizen nationals as diplomats representing a foreign country to the United States. The State Department permits such individuals to represent a foreign country in its diplomatic mission at United Nations Headquarters in New York City, but while in such positions they enjoy only official acts immunity and not diplomatic immunity. Thus, an individual wishing to assume a diplomatic or consular position in the United States may choose to relinquish U.S. citizenship. One early example of this, which was described at the time as the first such case in U.S. diplomatic history, was Oskar R. Lange's decision to renounce citizenship in 1945 to become the Polish ambassador to the United States.