Once an immigrant has been a lawful permanent resident (LPR) green card holder for five years, or three if married to a US citizen, he or she can apply for US citizenship through the naturalization process. The applicant must meet several US citizenship requirements such as length of permanent residence, length of physical presence in the US, good moral character and knowledge of English and basic US civics. A citizenship lawyer can assist in obtaining US citizenship by preparing a complete and accurate US citizenship application and attending the citizenship interview. Read more about US Citizenship & Naturalization.