Every country has its own laws regarding dual citizenship. The United States allows its citizens to hold a second nationality with any nation the individual qualifies to hold one with, whether earned through descent, marriage or residency. There is nothing you need to do with the U.S. government when you apply for a second citizenship. You can never lose your U.S. citizenship unless given up voluntarily in the presence of a U.S. diplomat. However, some countries require the denouncement of former citizenship before granting the new one.
Qualify for a second citizenship. Citizenship law is different in all countries; for instance, while citizenship through grandparent ancestry is possible in Ireland, it is not possible in say Guatemala. You must research the citizenship laws of the country of your particular interest before applying. Most countries allow citizenship through descent of a parent, through marriage and through a completed duration of residency.
Complete the forms, compile the necessary documents and pay the application fee. Find citizenship forms at the country's citizenship or immigration service department. In the U.S., this body is the United State Citizenship and Immigration Services, or USCIS. You must apply through the bureau responsible for citizenship in the country in which you are applying. Some countries allow for application outside of the country, while others do not. Required documents usually include copies of your visas, marriage certificate, birth certificate, residency card, photos and proof of decent (if applicable).
Attend an oath and flag swearing ceremony. In virtually all cases, earning a new citizenship is accompanied by a ceremony swearing allegiance to your new country of citizenship. This is usually done in a government office of the nation of citizenship or at one of the nation's foreign embassies. A certificate of citizenship usually is granted at the ceremony.