A Taxpayer Identification Number (TIN) is a unique set of numbers used for tax purposes in the United States and in other countries under the Common Reporting Standard. In the United States, it is also known as a Tax 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. Some examples of TINs include:

• Social Security number (SSN)
• Individual Taxpayer Identification Number (ITIN)
• Employer Identification Number (EIN)
• Adoption Taxpayer Identification Number (ATIN)
• Preparer Tax Identification Number (PTIN)

A TIN is mandatory for anyone filing annual tax returns with the IRS, which the agency uses to track taxpayers. Filers must include the number on tax-related documents and when claiming benefits or services from the government. TINs are also required for other purposes, such as identifying taxpayers and allowing entities to invest their money across the Union in countries in the European Union.