The requirements of obtaining US citizenship are listed below:

1) Applicant must be at least 18 years old.

2) Applicant must have been lawfully admitted to the United States for permanent residence.

3) Immediately preceding the filing of the application, he or she:
   has been lawfully admitted for permanent residence;
   has resided continuously as a lawful permanent resident in the U.S. for at least 5 years prior to filing with no single absence from the United States of more than one year;
   has been physically present in the United States for at least 30 months out of the previous five years (absences of more than six months but less than one year shall disrupt the applicant's continuity of residence unless the applicant can establish that he or she did not abandon his or her residence during such period); and
   has resided within a state or district for at least three months.

4) Applicant must show that he/she has been a person of good moral character for the statutory period (typically five years or three years if married to a U.S. citizen or one year for Armed Forces expedite) prior to filing for naturalization. However, the INS is not limited to the statutory period in determining whether an applicant has established good moral character.

5) Applicant must show that he/she is attached to the principles of the Constitution of the United States.

6) Applicant must be able to read, write, speak, and understand words in ordinary usage in the English language. Applicants exempt from this requirement are those who on the date of filing:
   have been residing in the United States subsequent to a lawful admission for permanent residence for periods totaling 15 years or more and are over 55 years of age;
  have been residing in the United States subsequent to a lawful admission for permanent residence for periods totaling 20 years or more and are over 50 years of age; or 
   have a medically determinable physical or mental impairment, where the impairment affects the applicant's ability to learn English.

7) Applicant must demonstrate a knowledge and understanding of the fundamentals of the history and of the principles and form of government of the United States. Applicants exempt from this requirement are those who, on the date of filing, have a medically determinable physical or mental impairment, where the impairment affects the applicant's ability to learn U.S. History and Government. Applicants who have been residing in the U.S. subsequent to a lawful admission for permanent residence for at least 20 years and are over the age of 65 will be afforded special consideration in satisfying this requirement.

8) To become a citizen, one must take the oath of allegiance. By doing so, an applicant swears to: 
    support the Constitution and obey the laws of the U.S.; 
    renounce any foreign allegiance and/or foreign title; and
    bear arms for the Armed Forces of the U.S. or perform services for the government of the U.S. when required.

In certain instances, where the applicant establishes that he or she is opposed to any type of service in armed forces based on religious teaching or belief, the INS will permit the applicant to take a modified oath.