WHAT IS DUAL NATIONALITY?
The Supreme Court of United States has stated that dual nationality is a "status long recognized in the law" and that "a person may have and exercise rights of nationality in two countries and be subject to the responsibilities of both. The mere fact that he asserts the rights of one citizenship does not without more mean that he renounces the other", Kawakita v. U.S., 717(1952).

HOW ACQUIRED
Dual Nationality results from the fact that there is no uniform rule of international law relating to the acquisition of nationality. Each country has its own laws on the subject, and its nationality is conferred upon individuals on the basis of its own independent domestic policy. Individuals may have dual nationality not by choice but by automatic operation of these different and sometimes conflicting laws.
The laws of the United States, no less than those of other countries, contribute to the situation because they provide for acquisition of U.S. citizenship by birth in the United States and also by birth abroad to an American, regardless of the other nationalities which a person might acquire at birth. For example, a child born abroad to U.S. citizens may acquire at birth not only American Citizenship but also the nationality of the country in which it was born. Similarly, a child born in the United States to foreigners may acquire at birth both U.S. citizenship and a foreign nationality.
The laws of some countries provide for automatic acquisition of citizenship after birth. For example, a U.S. citizen may acquire another nationality merely by marrying a citizen of certain foreign countries. In addition, some countries do not recognize naturalization in a foreign state as grounds for loss of citizenship. A person from one of those countries who is naturalized in the United States keeps the nationality of the country of origin, despite the fact that one of the requirements for naturalization in this country is a renunciation of other nationalities.
The automatic acquisition or retention of a foreign nationality does not affect U.S. citizenship; however, the acquisition of a foreign nationality upon one's own application may cause loss of U.S. citizenship under Section 349(a)(1) of the Immigration and Nationality Act (8 U.S.C. 1481). In order for loss of nationality to occur under Section 349(a)(1), it must be established that the naturalization was obtained with the intention of relinquishing U.S. citizenship. Such an intention may be shown by a person's statements or conduct. If the U.S. Government is unable to prove that the person had such an intention when applying for and obtaining the foreign citizenship, the person will have both nationalities.

CURRENT LAW AND POLICY
United States law does not contain any provisions requiring U.S. citizens who are born with dual nationality or who acquire a second nationality at an early age to choose one nationality or the other when they become adults, Mandeli v. Acheson, 344 U.S. 133 (1952). The current nationality laws of the United States do not specifically refer to dual nationality.
While recognizing the existence of dual nationality and permitting Americans to have other nationalities, the U.S. Government does not endorse dual nationality as a matter of policy because of the problems which it may cause. Claims of other countries on dual national U.S. citizens often place them in situations where obligations to one country are in conflict with the laws of the other. In addition, their dual nationality may hamper efforts to provide diplomatic and consular protection to them when they are abroad. In general it is considered that while a dual national is in the other country of which the person is a citizen, that country has a predominant claim on the person.

ALLEGIANCE TO WHICH COUNTRY
Like Americans who possess only U.S. citizenship, dual national U.S. citizens owe allegiance to this country and are obliged to obey its laws and regulations. Such persons usually have certain obligations to the foreign country as well. Although failure to fulfill such obligations may have no adverse effect on the person while in the United States because the foreign country would have few means to force compliance under those circumstances, the person might be forced to comply with those obligations or pay a penalty if the person goes to the foreign country. In cases where a dual national encounters difficulty in a foreign country of which the person is a citizen, the ability of U.S. Foreign Service posts to provide assistance may be quite limited since the foreign countries may not recognize the dual national's claim to U.S. citizenship.

WHICH PASSPORT TO USE
Section 215 of the Immigration and Nationality Act (8 U.S.C. 1185) requires U.S. citizens to use U.S. passports when entering or leaving the United states unless one of the exceptions listed in Section 53.2 of Title 22 of the Code of Federal Regulations applies. Dual nationals may be required by the other country of which they are citizens to enter and leave that country using its passport, but do not endanger their U.S. citizenship by complying with such a requirement.