An applicant for US citizenship must meet the following requirements:
Must be admitted to the United States as a lawful permanent resident (LPR). There is only one exception to this requirement: If an applicant has served in the US armed forces during war, that person may be naturalized without first becoming a permanent resident if they were in the United States upon induction or enlistment into the US military.
Continuous residence in the US for at least five years immediately preceding the applicant's filing for naturalization. Continuous residence is not the same thing as physically present here. That is, one must maintain their status as a legal permanent resident but not necessarily be physically inside the borders of the US to accomplish this. For example, if one is overseas for a portion of this period, maintaining an address location and paying one's state and federal taxes may help ensure continuity of residence for this requirement. Also, if overseas for any more than a few months, it may be advisable to obtain a travel document prior to departing. This may be done on Form I-131. Only three years continuous residence are required if the applicant is filing for US citizenship based upon marriage. This exception applies if you are the spouse of a US citizen and have been married for three years; are the battered spouse of a US citizen (even if you are separated or divorced); are a refugee or political asylee; in the US military or are a widow or widower of someone in the US military; or are a spouse of a US citizen in particular overseas jobs.
Actual physical residence (within the state in which the petition is filed) during at least the three months immediately before filing for US citizenship is another requirement.
Physical presence within the US for a total of at least one half of the period of required continuous residence. That is, two and a half years for most applicants and one and a half years for spouses of US citizens.
Continuous residence (but not necessarily physical presence) in the United States from the date of filing the naturalization application up to the date of being sworn in as a US citizen.
The ability to read, write and speak ordinary English unless they are physically unable to do so due to a disability such as being blind or deaf, or suffer from a developmental disability or mental impairment. Those over 50 years old on the date of filing who have lived here for a total of at least 20 years after admission as a permanent resident and those who are over 55 and have been legal permanent residents for at least 15 years are also exempt from this requirement.
A basic understanding of the fundamentals of US history and government. There is an oral test that covers fundamentals of US history and government and it is required for naturalization.
Good moral character and an affinity for the principles of the US Constitution. Good moral character is reflected in the applicant's behavior before applying for US Citizenship Through Naturalization. Good moral character is demonstrated by paying taxes and having a clean criminal record, for example, and is an important part of qualifying for naturalization.
Applicants should be at least 18 years of age at the time of filing. Certain exceptions exist, however, for the children of other permanent residents who are seeking naturalization.