Unless you are born to US citizen parents or are born in the US, you must apply for US citizenship through naturalization. To do so, you must meet the requirements for US naturalization. In most cases, to become a US citizen, you must:
1) Be the age of majority (at least 18 years old)
2) Meet residency requirements. This means that you must have resided in the US as a legal immigrant in the USA for a specific time. The exact amount of time varies depending on your specific circumstances. For example, most applicants must have resided in the US as lawful green card holders for at least five years. If you are married to a US citizen, however, your residency period is three years. Refugees must generally wait four years. If you move often or spend considerable time outside of the US, this can affect your citizenship application. However, the USCIS does make provisions for members of the military and for students, who may face reduced residency requirements. In addition to having to remain in the US for a specific amount of time, you must keep in mind that you must remain in one US territory or state for a specific period of time before applying to become a US citizen. In most cases, you must have lived for at least three months in the state or territory from which you are applying.
3) Be of “good moral character.” Generally, this means that you must not have been convicted of certain serious crimes and have shown that you can be a good US citizen. If there is something in your past that you feel may bar you from becoming a US citizen, you may wish to consult with a qualified US immigration attorney before applying for citizenship.
4) Read, write, and speak English. Your English language skills will be tested during the citizenship interview and test. In some cases, elderly persons who have resided as lawful permanent citizens in the US for many years may not need to meet these language requirements.
5) Understand the basics of US civics, government, and history. Your knowledge in these subjects will be tested during the citizenship test.
6) Understand and agree with the U.S. Constitution.