If you are applying for a green card, naturalization, or some other U.S. immigration benefit, U.S. Citizenship and Immigration Services (USCIS) will require you to submit a fee for "biometrics." It will then call you in for a biometrics appointment, usually a few weeks before you attend the interview at which your application is decided upon (if an interview is required).
Even people who already have a green card, but are applying for a renewal after the card itself expires, must get biometrics done.
In most cases, USCIS will require that you attend your biometrics appointment at a USCIS-authorized "Application Support Center." For a list of ASCs, see the USCIS Service and Office Locator. In some nonurban areas of the United States, USCIS also offers mobile biometrics vans.
The notice USCIS sends you about your biometrics appointment will tell you what to bring with you: typically a copy of the appointment notice and some kind of photo identification, such as a drivers' license or your passport. If you have only an expired passport, do your best to get a new one as soon as possible. If you are still waiting for a new one when your appointment is scheduled, bring a letter or receipt notice from your home country’s embassy stating that your passport renewal is in progress.
In many cases the notice will tell you what you can’t bring into the building with you. Don’t expect to bring in a phone, camera, or any food or drink.
If you cannot make it at the scheduled time or on the scheduled day, you can ask to be rescheduled. (If you know right away you won’t be able to make it, the appointment notice tells you how to make the request,)
During normal (non-COVID) times, at the less-busy ASCs, the timing was somewhat flexible, so if you showed up an hour early, it would take you regardless of what your appointment time is. But that's less likely to happen while the pandemic is ongoing, as the offices try to strictly control traffic flow.
It’s never good to show up later than your scheduled time, but if an emergency causes you to be an hour late, try showing up and explain, asking to be processed right then anyway.
In scientific terms, "biometrics" means anatomical or physiological data by which a person can be uniquely identified. At your biometrics appointment, USCIS will most likely collect your fingerprints, take your photo, and have you sign your name for electronic capture.
The actual process takes about 20 minutes, though you may have to wait a while after you arrive. A number of people might have received the exact same appointment time as you did. As a general rule, everyone who was given the same appointment time will probably be called in on a first-come, first-served basis.
Once you arrive at the ASC, you might be given a number showing your place in line, or you might be asked to fill out and hand in a short form letting the ASC employees know you’re there. They’ll call your wait-list number or your name when it’s your turn.
At the end of the biometrics appointment, you will be given a stamp on your appointment notice confirming that you attended. Keep this document safe, in case you are later asked for it or USCIS cannot find its record stating that you indeed came to the appointment.
By the way, if you have questions about your case; such as when you are likely to be called in for an interview; this is not the place to ask them. The people who collect biometrics do not have access to your file, and cannot give you advice or information about your case.
Your fingerprints will be sent on for review by the U.S. Federal Bureau of Investigation (FBI), which will check them against records held by the police as well as by USCIS (which often takes the fingerprints of people caught crossing the border illegally). The FBI will send a report to USCIS to confirm your identity and to show whether you have committed any crimes or immigration violations that might make you inadmissible, deportable, or otherwise ineligible for the benefit that you seek.
If you think you might have a criminal record but are not sure, consult a lawyer. Some but not all crimes make you ineligible for immigration benefits.
You won’t discover until you get to your interview what the FBI report says about you. The lawyer can help you request a separate fingerprint report from the FBI and deal with whatever it shows, to help you get your green card, citizenship, or other benefit.