An Alien Registration Number (also known as the “A-number” or “USCIS number”) is a number assigned to anyone applying to live permanently in the United States, namely green card applicants.
You will typically receive your Alien Registration Number when you apply for a green card, but the timeline differs depending on if you’re applying from within or outside the United States, and whether you’re married to a U.S. citizen or green card holder (lawful permanent resident).
Once U.S. Citizenship and Immigration Services (USCIS) assigns you an Alien Registration Number, the number will appear on all documents the agency sends to you.
On most forms, you will see it labeled as “A#” near the top of the page. Learn more with our in-depth guide about the Alien Registration Number.