What Is the Social Security Federal Identification Number?

The Social Security Administration (SSA) is a world of numbers. They use cardinal numbers to count things, ordinal numbers to note the position of one thing to another and nominal numbers to identify a person, place or thing – thus the term "identification number." One reason SSA relies on nominal numbers, rather than names, to identify individuals is that while names are hardly unique, a number with a sufficient number of digits can be unique in a given set, such as one in a million, one in a trillion and so on.

Consequently, the SSA has not just one set of identifying numbers for American citizens, but many. To make things more interesting, or at least more unique, some of the identifier sequences they use have numeric and alphanumeric characters.

The Taxpayer Identification Number (TIN), which consists of nine digits, represents a person or business that is subject to the tax laws of the United States. The Internal Revenue Service (IRS) uses this number as it administers these tax laws.

Both the Social Security Administration and the Internal Revenue Service can issue a tax identification number. When issued by the SSA, it takes the form of a Social Security number. If the Internal Revenue Service issues the identifier, it's a tax identification number. The latter can take multiple forms.

Issued by the Social Security Administration, the Social Security number identifies an individual and serves to associate relevant wage and self-employment earnings records with that person. The Social Security number serves as a tax identification number for Internal Revenue Service purposes. To obtain an SSN, complete the Form SS-5 and take it to any Social Security office. See instructions for completing the Form SS-5 here.

An Employer Identification Number, also referred to as a Federal Employee Identification Number (FEIN), is a nine-digit tax identification number that's assigned to a business by the Internal Revenue Service. You can apply for an EIN online. See instruction for applying for an EIN here.

Read More: How to Find Your Employer Identification Number

The Individual Taxpayer Identification Number (ITIN) is a nine-digit TIN that begins with the number "9." The ITIN is issued by the Internal Revenue Service to some resident and nonresident aliens and their dependents in lieu of Social Security numbers. To obtain an ITIN, complete the IRS Form W-7 and return it to the IRS. See instructions for completing the IRS Form W-7A here.

The Adoption Taxpayer Identification Number is a nine-digit tax identification number that the Internal Revenue Service assigns to a child in a domestic adoption when the assignment of the child's Social Security Number is pending. To obtain an ATIN, complete the IRS Form W-7 and return it to the IRS. See instructions for completing the IRS Form W-7A here.

The Preparer Tax Identification Number is a four- to six-digit number that the IRS assigns to a for-fee tax return preparer who prepares or provides substantial assistance in the preparation of a U. S. federal tax return, a claim for refund or other forms, with some exceptions. To obtain a PTIN, complete the IRS Form W-12 and return it to the IRS. See instructions for completing the IRS Form W-12 here.

Taxpayers acquire a taxpayer identification number to support the IRS in its efforts to administer tax laws. Depending on the type of TIN you require, either the Social Security Administration or the IRS will issue the number. Whereas the SSA issues the Social Security number, the IRS issues all other TINs.