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.
The U.S. Government acknowledges 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 the United States. Dual nationals may also be required by the foreign country to use its passport to enter that country. Use of the foreign passport does not put into jeopardy your U.S. citizenship. Most countries permit a person to renounce or otherwise lose citizenship.
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 over 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.
If you are a U.S. citizen who has acquired or plans to acquire Canadian citizenship, and you intend to relinquish your U.S. citizenship or wish to relinquish your U.S. citizenship, please discuss with the U.S. Embassy or Consulate the procedures necessary to formalize this. There will be a US$450 fee to document formal renunciation of U.S. citizenship. More information relating to the loss of citizenship is on this Travel.State.Gov information sheet. In addition, please review this page, regarding the making of a citizenship claim.
Information on losing foreign citizenship should be obtained from the foreign country's Embassy and Consulates in the United States or Canada.