A Social Security number (SSN) is a nine-digit number issued to U.S. citizens, permanent residents, and temporary residents under section 205 of the Social Security Act, codified as 42 U.S.C. § 405. The SSN is used to track income and determine benefits, and it is assigned by the Social Security Administration (SSA) . The SSN consists of three parts: the area number, the group number, and the serial number. The area number is assigned based on the geographical region, and prior to 1972, cards were issued in local Social Security offices around the country, and the area number represented the state in which the card was issued. Since 1972, the SSA has been issuing SSNs and cards centrally from Baltimore, and the area number assigned has been based on the ZIP code in the mailing address provided on the application for the original Social Security card. The group number has no special geographic or data significance, and it is used to break the numbers into blocks of convenient size for SSA’s processing operations and for controlling the assignments to the states. The serial number represents a numerical series from 0001 to 9999 within each group.

The SSN is used to report wages to the government, track Social Security benefits, and for other identification purposes. To get an SSN, one must file Form SS-5 with the Social Security Administration. The SSN is susceptible to illegal use by those involved in identity theft and fraud. If an F or M student (or dependent) is ineligible to receive an SSN but receives non-wage income while in the United States (e.g., scholarships, grants, interest on stocks, gambling/lottery winnings), they must apply for an Individual Taxpayer Identification Number (ITIN) .