Note: I didn't write the following. I just found it somewhere and adapted it for my website. You can get the original file I worked from (the origins of which I forget). I believe there are now more up to date sources elsewhere.

SSA has continually emphasized the fact that the SSN identifies a particular record only and the Social Security Card indicates the person whose record is identified by that number. In no way can the Social Security Card identify the bearer. From 1946 to 1972 the legend "Not for Identification" was printed on the face of the card. However, many people ignored the message and the legend was eventually dropped. The social security number is the most widely used and carefully controlled number in the country, which makes it an attractive identifier. Can YOU make a payphone salute?

With the exception of the restrictions imposed on Federal and some State and local organizations by the Privacy Act of 1974, organizations requiring a unique identifier for purposes of controlling their records are not prohibited from using (with the consent of the holder) the SSN. SSA records are confidential and knowledge of a person's SSN does not give the user access to information in SSA files which is confidential by law.

Many commercial enterprises have used the SSN in various promotional efforts. These uses are not authorized by SSA, but SSA has no authority to prohibit such activities as most are not illegal. Some of these unauthorized uses are: SSN contests; skip-tracers; sale or distribution of plastic or metal cards; pocketbook numbers (the numbers used on sample social security cards in wallets); misleading advertising, commercial enterprises charging fees for SSN services; identification of personal property.

The Social Security Number (SSN) is composed of 3 parts, XXX-XX-XXXX, called the Area, Group, and Serial. For the most part, (there are exceptions), the Area is determined by where the individual applied for SSN (before 1972) or resided at time of application (after 1972). The areas are assigned follows:

As the Areas assigned to a locality are exhausted, new areas from the pool are assigned. This is why some states have non-contiguous groups of Areas.

The Group portion of the SSN has no meaning other than to determine whether or not a number has been assigned. SSA publishes a list every month of the highest group assigned for each SSN Area. The order of assignment for the Groups is: odd numbers under 10, even numbers over 9, even numbers under 9 except for 00 which is never used, and odd numbers over 10. For example, if the highest group assigned for area 999 is 72, then we know that the number 999-04-1234 is an invalid number because even Groups under 9 have not yet been assigned.

The Serial portion of the SSN has no meaning. The Serial is not assigned in strictly numerical order. The Serial 0000 is never assigned.

Before 1973, Social Security Cards with pre-printed numbers were issued to each local SSA office. The numbers were assigned by the local office. In 1973, SSN assignment was automated and outstanding stocks of pre-printed cards were destroyed. All SSNs are now assigned by computer from headquarters. There are rare cases in which the computer system can be forced to accept a manual assignment such as a person refusing a number with 666 in it!

A pamphlet entitled "The Social Security Number" (Pub. No. 05-10633) provides an explanation of the SSN's structure and the method of assigning and validating Social Security numbers.