An Individual Taxpayer Identification Number (ITIN) is a tax processing number issued by the Internal Revenue Service (IRS) to individuals who are required to have a U.S. taxpayer identification number but who do not have, and are not eligible to obtain, a Social Security Number (SSN) from the Social Security Administration. The ITIN is a nine-digit number beginning with the number “9” and formatted like an SSN (i.e., 9XX-XX-XXXX) . It is issued to individuals who need to report income but are ineligible to obtain a valid SSN, such as foreign nationals, undocumented immigrants, and their dependents or spouses.

Receiving an ITIN number does not in itself confer the right to work and receive income in the United States. ITINs are used to file tax returns and pay taxes, and they are also used by real estate brokers to facilitate mortgages for unauthorized aliens and foreign investors in United States real estate.

In 2012, the IRS indicated that ITINs would expire after five years, but in 2014, the IRS amended that policy to expire ITINs only if the numbers had not been used in the last five years. Under this revised policy, effective in 2016, all ITINs must be used to file a return or they will expire and be reassigned. This now includes those issued before 2013. The policy has since been revised again so that ITINs would expire after three years of non-use.