What is a US social security number?

A social security number (or “SSN”) is a nine-digit number issued to US citizens, permanent residents, and temporary (working) residents. It is the primary identifier for individuals, used by government agencies, private enterprises, and financial institutions.

Only certain types of individuals are eligible for an SSN. Individuals who are not eligible for an SSN may be eligible to receive a US individual tax identification number (or “ITIN”). An ITIN is issued by the IRS instead of the Social Security Administration and is designed to provide a tax processing number for those who are not eligible for an SSN but still need to comply with US tax laws. Unlike an SSN, an ITIN expires if not used on a federal tax return for three consecutive years.

Like an SSN, an ITIN is often used in financial transactions. Consequently, the IRS has strict rules governing eligibility to receive an ITIN. To obtain an ITIN, you must have a need for an ITIN. This may be the case, for example, if you have US sourced income (e.g., dividends from a US company or income from services performed in the US) or if you have engaged in a transaction involving US real property.

Because the SSN is used in connection with credit and finance, it is held in strict confidence. If you have access to an individual’s SSN (for example, because that person is employed by you or your affiliate), then you should exercise the highest precautions to guard against its misappropriation. It should not be sent by email. If it must be sent electronically, it should be sent with a password or by other protected document. It should also be revealed only when absolutely necessary and to only to people with a need to know.