In the United States, a Social Security number (or SSN) is a number issued to citizens, permanent residents, and temporary (working) residents under section 205(c)(2) of the Social Security Act, codified as 42 U.S.C. § 405(c)(2). The number is issued to an individual by the Social Security Administration, an agency of the federal government. Ostensibly, its primary purpose is tracking working individuals for taxation purposes and to track Social Security benefits. However, in recent years, the SSN has become a de facto national identification number, even though it is not supposed to be used as a form of identification.
Contrary to popular belief, there is still no law directly requiring a natural born US Citizen to apply for a Social Security number to live or work in the United States. Although a handful of people still live this way, it is becoming ever increasingly difficult to engage in normal acts of commerce or banking activities without providing one. Such prohibitions against persons that refuse to enter into what amounts to a voluntary government program, raises a variety of constitutional concerns.
Here is a more detailed explanation of Social Security’s five-step process to determine if an individual qualifies for Social Security Disability Insurance: