Citizenship of the United States
A person who is considered a citizen by more than one nation has "dual citizenship". It is possible for a United States citizen to have dual citizenship; this can be achieved in various ways, such as by birth in the United States to a parent who is a citizen of a foreign country (or in certain circumstances the foreign nationality may be transmitted even by a grandparent) by birth in another country to a parent(s) who is/are a United States citizen/s, or by having parents who are citizens of different countries. Anyone who becomes a naturalized U.S. citizen is required to renounce any prior "allegiance" to other countries during the naturalization ceremony; however, this renunciation of allegiance renunciation of citizenship to those countries.
United States Citizenship and Immigration Services
USCIS focuses on two key points on the immigrant's journey towards civic integration: when they first become permanent residents and when they are ready to begin the formal naturalization process. A lawful permanent resident is eligible to become a citizen of the United States after holding the Permanent Resident Card for at least five continuous years, with no trips out of the United States lasting 180 days or more. If, however, the lawful permanent resident marries a U.S. citizen, eligibility for U.S. citizenship is shortened to three years so long as the resident has been living with the spouse continuously for at least three years and the spouse has been a resident for at least three years.