To apply for naturalization, the spouse of a U.S. citizen must file the application for naturalization, Form N-400, according to the U.S. Citizenship and Immigration Services. Other requirements include already having a permanent resident visa, having lived in the United States for at least three years prior to the time of application, and being married to and living with the citizen spouse during that entire period of time.
Additional requirements for naturalization include being at least 18 years old, being fluent in oral and written English, and being of good moral character, states the USCIS. The applicant must be knowledgeable regarding U.S. history and government, demonstrate an attachment to the principles of the U.S. Constitution and desire good order and happiness for the United States. More specific residency requirements include a physical presence within the United States for at least 18 months of the previous three-year period, continuous residency from the time of application until naturalization, and residency in the state or USCIS district of jurisdiction for three months prior to filing the application.
Under certain circumstances, the spouse of a U.S. citizen working abroad for the government may also qualify for naturalization, says the USCIS. The agency waives some of the residency requirements in these cases; however, the applicant still must have permanent resident status in the United States.