The U.S. Citizenship and Immigration Services website provides a list of requirements that immigrants must meet to receive American citizenship. Most applicants are foreigners who possess "green cards" and are already living in the United States.
As of 2015, naturalization applicants must possess a green card for at least five years and live in the United States for at least 30 months during that period, prior to filing the application, states the U.S. Citizenship and Immigration Services. They must be at least 18 years of age and reside continuously in the United States after applying.
Applicants must have written and verbal fluency in English, pass a test on American history and government and have good moral character to qualify for citizenship, the website states. Immigrants also may attain citizenship through marriage to a U.S. citizen or service in the military or through their citizen parents.