The Supreme Court of the 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 [sic] asserts the rights of one citizenship does not without more mean that he renounces the other" (see Kawakita v. U.S., 343 U.S. 717 [1952] ).

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 (see Mandoli 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 upon dual-national U.S. Citizens often place them in situations where their 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 while they are abroad.  It generally 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.  In cases where a dual national encounters difficulty in a foreign country of which the person is a citizen, the ability of the U.S. Government to provide assistance may be quite limited since many foreign countries may not recognize the dual national's claim to U.S. Citizenship.

Section 215 of the Immigration and Naturalization 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.

Visit the Department of State website about "Advice about Possible Loss of U.S. Citizenship and Dual Nationality."