If you are a permanent resident (“green card holder”) and a spouse of a U.S. Citizen, you can apply for citizenship three years after approval of your Adjustment of Status. Your approval may be noted via any of the following: approval notice (I-797), on your passport (I-551 stamp and date), or your green card (“resident since” date). The three year count down begins with that date.
If you are not married to a U.S. citizen, you can apply for citizenship five years after the approval of your adjustment of status. (There are exceptions for members of the U.S. armed services, which will be discussed in a separate post.)
It is not enough to simply be a green card holder for the required number of years. You must also be in “continuous residence”
during that time. “Continuous residence” means that you have not left the United States for a long period of time. If you leave the U.S. for more than six months, it is likely that you interrupted your continuous residence. In almost all cases, if you leave the United States for one year or more, you have disrupted your continuous residence and may not be eligible to apply for U.S. citizenship.