Dual citizenship means that a person is a citizen of two countries at the same time. This situation is rather complex, because each of the two countries has its own laws and all its citizens are supposed to abide by these laws. Since the person has two citizenships, he or she is supposed to abide by the laws of the both countries. The problem arises when laws of one country contradict laws of the other country, or when one of the countries does not recognize a dual citizenship.
Dual citizenship may emerge either automatically or by choice. For instance, if a child is born in the U.S.A. to foreign parents, then he or she may have the U.S. citizenship (by birth) and a foreign citizenship of his or her parents or one of the parents, or even both of them (three citizenships in total), if the parents have different citizenships. If a person is naturalized and keeps his or her other citizenship, then the person will have two citizenships by choice provided that both of the countries recognize dual citizenship. Otherwise the person will have to choose one or another citizenship.
If a person gets another citizenship automatically, he or she is not going to lose his or her U.S. citizenship. However, if a U.S. national is going to apply for a foreign citizenship, i.e. is going to get it by choice, he or she may lose the U.S. citizenship. Under the U.S. law the U.S. national will lose his or her citizenship, if he or she applies to a foreign citizenship by choice and with the intention to give up his or her U.S. citizenship. Such intent should be demonstrated either by certain statements or personal conduct.
The U.S. Government recognizes the dual citizenship, but doesn’t encourage it, because of the problems that may arise as a result of conflicts between the U.S. and foreign laws. Since either country has the right to enforce its laws, such conflicts are unavoidable.