Social Security Number Definition

A social security number is a 9-digit number issued in the US to citizens, permanent residents, and some temporary working residents. The number is issued by the federal government’s Social Security Administration. Social security numbers have been issued since 1936; since about 1986 social security numbers have been, generally, issued within a few days of birth (most current applications for birth certificates have a check box to also request social security numbers). The first three digits of the social security number represent a geographical area of issue (not necessarily the birth area), the second two digits are a group number, and the final four digits are a serialized number.