To become U.S. citizens, foreigners must first become permanent residents (green card holders). Legal residents can apply for U.S. citizenship, but after five years of being green card holders. For immigrants married to U.S. citizens, from green card to U.S. citizenship will take around three years.
People who received their resident cards based on having received asylum status can apply for naturalization after four years from the date on which they received their resident cards.
There are few requirements the permanent residents need to meet in order to apply for U.S. citizenship. Applicants need to show that they were present in the U.S. for 30 months within the five year period. Likewise, people applying for U.S. citizenship based on their marriage to U.S. citizens, must establish that they were present in the country for 18 months within the three year period.
Extended absences from the country are likely to break the applicant’s continuous residence. In general, a person who seeks to apply for U.S. citizenship, must not have spent more than a year outside the U.S.
People who had stayed abroad for a period of six months need not worry as such brief trips may not break their continuous residence. People who had stayed abroad for more than six months and less than a year, may not be able to apply for U.S. citizenship. But they may be permitted to file their citizenship applications if they establish that they have not broken their continuous residence, by submitting documents that USCIS requires.
Those who have been abroad for more than a year and who cannot apply for citizenship, can apply later after they meet the residency requirement. This applies to both those who are applying under the common path to U.S. citizenship and under the three year rule.
Certain applicants are eligible for a reduced period of continuous residence and some applicants may be exempt from the continuous residence requirement. This applies to those who are working abroad for the U.S. government, recognized American Institutions of research, public international organizations and to the contractors of the U.S. government. Such applicants can preserve their continuous residence for naturalization purposes. To do so, they need to file Form N-470, Application to Preserve Residence for Naturalization Purposes.