Naturalization is the lawful way of acquiring citizenship. Generally speaking, in order to qualify for naturalization, a person must first be a Lawful Permanent Resident (LPR). There are some exceptions for military personnel. The person applying must be at least 18 years old, have resided continuously fin the U.S. for five years after permanent residency. This requirement is reduced to three years if the person gained their permanent residency status based on a marriage to a U.S. citizen. It is necessary for the applicant to have a residency for at least three months prior to the application for citizenship in the state in which they are filing their petition. It is also necessary that the person is physically present in the United States for at least half the residency period. In addition, it is necessary to maintain a continuous residency in the United States during the naturalization application process. There is also a requirement of good moral character and a minimal ability to read and write english, as well as understand the basic history and principles of government of the United States.