An individual is eligible for naturalized U.S. citizenship if she is 18 years or older and has been a permanent resident for at least five years, according to U.S. Citizenship and Immigration Services. An applicant must demonstrate five or more continuous years of U.S. residency immediately preceding the application date.
To be eligible for naturalization, an applicant must also prove she was physically present in the country for at least 30 months out of the five years immediately preceding the application date, explains U.S. Citizenship and Immigration Services. She must be able to read, write and speak basic English. She must have a basic understanding of civics.
Individuals who are born in the United States or in certain territories and subject to the jurisdiction thereof, have at least one U.S. citizen parent or meet certain other criteria set by the U.S. Department of State are eligible for citizenship at birth, according to the U.S. Department of Homeland Security.