According to the Social Security Administration, the Social Security number (SSN) was created in 1936 for the sole purpose of tracking the earnings histories of U.S. workers, for use in determining Social Security benefit entitlement and computing benefit levels. Over the years it has become the chief means of identifying and gathering information about an individual for the government and private sector.
You have control over who gets your Social Security number. It is not necessary to provide it to everyone who asks, so make sure you understand why they need it and how they will be using the information. Remember the fewer people who have your Social Security number, the better for you.