What are the requirements to become a citizen of the United States?

Generally, to become a citizen of the United States you must have been a permanent resident, which means have a blue card for five years, and have lived in the United States for most of that time, generally without any trips longer than six months in length. There are some exceptions where if you are married to a US citizen it could be after three years. If you serve in the armed forces at a time of conflict it could be immediately. There are other circumstances such as armed forces enlistment where you don’t even need to have residency or a blue card in order to apply for naturalization, which is citizenship.