A Tax Identification Number (TIN) is a unique identifying number used for tax purposes in the United States and other countries under the Common Reporting Standard. In the United States, it is also known as a Taxpayer Identification Number or Federal Taxpayer Identification Number. A TIN may be assigned by the Social Security Administration or by the Internal Revenue Service (IRS) . Any government-provided number that can be used in the US as a unique identifier when interacting with the IRS is a TIN, though none of them are referred to exclusively as a Taxpayer Identification Number.

There are several types of TINs in the US, including:

• Social Security Number (SSN): This is a nine-digit number issued to individuals by the Social Security Administration. It is the most popular tax ID number.

• Individual Taxpayer Identification Number (ITIN): This is a nine-digit tax ID number for nonresident and resident aliens, their spouses, and their dependents who cannot get a Social Security number and are required to file taxes or have a tax ID number.

• Employer Identification Number (EIN): This is a tax ID number for businesses that have employees, are corporations or partnerships, withhold taxes on income paid to nonresident aliens, have Keogh plans, or are involved with certain types of organizations.

A taxpayer must provide their TIN on all tax returns and other documents sent to the IRS. They must also provide their identification number to other persons who use the identification number on any returns or documents that are sent to the IRS.