In the United States, an alien number is an identification number the U.S. Citizenship and Immigration Services (USCIS) assigns to foreign nationals. An alien number is also known as an alien registration number, A-number or USCIS number.
The term "alien" refers to a non-citizen of the U.S. Prospective employers can use the alien number to verify a non-citizen applicant's eligibility to work. The online program known as E-Verify crosschecks an alien's employment qualifications against federal and state records. A non-citizen's Permanent Resident Card, Employment Authorization Document and U.S. Machine Readable Immigration Visa all contain the alien registration number.