Legal Definitions - taxpayer identification number (TIN)

A taxpayer identification number (TIN) is a unique nine-digit number assigned to individuals or entities by the Internal Revenue Service (IRS) for tax purposes. TINs are used to identify and track taxpayers and are mandatory for filing tax returns or claiming treaty benefits.

There are several types of TINs, including:

• Social Security Number (SSN)
• Employer Identification Number (EIN)
• Individual Taxpayer Identification Number (ITIN)
• Taxpayer Identification Number for Pending U.S. Adoptions (ATIN)
• Preparer Taxpayer Identification Number (PTIN)

The Social Security Administration (SSA) issues the SSN, while the IRS issues all other TINs.

For example, if you are an employee, your employer will use your SSN to report your wages to the IRS. If you are a business owner, you will need an EIN to file your business taxes. If you are a nonresident alien who earns income in the United States, you will need an ITIN to file your tax return.

These examples illustrate how TINs are used to identify and track taxpayers for tax purposes.