This article is from the FAQ, by with numerous contributions by others.
The concept of dual nationality means that a person is a citizen of two
countries at the same time. Each country has its own citizenship laws
based on its own policy.Persons may have dual nationality by automatic
operation of different laws rather than by choice. For example, a child
born in a foreign country to U.S. citizen parents may be both a U.S.
citizen and a citizen of the country of birth. A U.S. citizen may acquire
foreign citizenship by marriage, or a person naturalized as a U.S. citizen
may not lose the citizenship of the country of birth.U.S. law does not
mention dual nationality or require a person to choose one citizenship
or another. Also, a person who is automatically granted another citizenship
does not risk losing U.S. citizenship. However, a person who acquires a
foreign citizenship by applying for it may lose U.S. citizenship.
In order to lose U.S. citizenship, the law requires that the person must
apply for the foreign citizenship voluntarily, by free choice, and with
the intention to give up U.S. citizenship. Intent can be shown by the
person's statements or conduct.The U.S. Government recognizes that dual
nationality exists but does not encourage it as a matter of policy because
of the problems it may cause. Claims of other countries on dual national
U.S. citizens may conflict with U.S. law, and dual nationality may limit
U.S. Government efforts to assist citizens abroad. The country where a
dual national is located generally has a stronger claim to that person's
allegiance. However, dual nationals owe allegiance to both the United
States and the foreign country. They are required to obey the laws of both
countries. Either country has the right to enforce its laws, particularly
if the person later travels there.Most U.S. citizens, including dual
nationals, must use a U.S. passport to enter and leave the United States.
Dual nationals may also be required by the foreign country to use its
passport to enter and leave that country. Use of the foreign passport
does not endanger U.S. citizenship.Most countries permit a person to
renounce or otherwise lose citizenship. Information on losing foreign
citizenship can be obtained from the foreign country's embassy and
consulates in the United States. Americans can renounce U.S. citizenship
in the proper form at U.S. embassies and consulates abroad.
Rules And Regulations Pertaining To The Employment Based Immigration