A Tax Identification Number, often referred to as a TIN, is a nine-digit government-issued identification number assigned to individuals, businesses and non-profit organizations in accordance with United States tax regulations. Tax identification numbers are used in tax laws, particularly those relating to income tax, estate tax, and gains derived from investment. It is used to identify taxpayers and track financial activities for tax purposes.

The Internal Revenue Service (IRS) issues tax identification numbers in the United States. However, the Social Security Administration is responsible for issuing Social Security Numbers, which are also classified as a form of tax identification number.

There are multiple types of tax identification numbers which are issued depending on a person or entity’s circumstances. Different identification numbers are issued to individuals, corporations, estates, trusts, partnerships and non-profit organizations.

Individual Taxpayers are typically issued Individual Taxpayer Identification Numbers (ITINs). This number is used to identify tax filers who do not yet possess a Social Security number, but are required to provide taxes. This includes immigrants, visa holders, and non-immigrant citizens who must file taxes on a yearly basis.

Employers are issued an Employer Identification Number (EIN) to identify businesses or companies for tax purposes. This number is necessary for payroll purposes, when hiring and filing taxes.

Estates are issued an Estate Tax Identification Number (ETIN) to identify the estate for tax purposes.

Adoption Taxpayer Identification Numbers (ATINS) are used to identify taxpayers who are not yet able to acquire a Social Security number for an adopted minor.

In general, all tax filers are required to include their tax identification number on all tax-related documents and when claiming benefits, such as tax refunds. Tax identification numbers are also necessary when submitting job applications and for applications for credit.

TINs play an important role in the US tax system, ensuring the filing of taxes and the payment of benefits is accurate and timely. Businesses, individuals and non-profit organisations should use and maintain their TIN numbers in a responsible manner to ensure compliance with US tax requirements.