An Individual Taxpayer Identification Number (or ITIN) is a United States tax processing number issued by the Internal Revenue Service. It is a nine-digit number that begins with the number 9 and has a 7 or 8 in the fourth digit, i.e. 9xx-7x-xxxx or 9xx-8x-xxxx. The IRS issues ITINs to individuals who are required to have a taxpayer identification number but who do not have, and are not eligible to obtain, a Social Security Number.

ITINs are issued regardless of immigration status because both resident and nonresident aliens may have Federal tax return and payment responsibilities under the Internal Revenue Code. Individuals must have a filing requirement and file a valid federal income tax return to receive an ITIN, unless they meet an exception.