The US government provides several types of identification numbers, all of which contain precisely nine digits. The US issues three primary types of TINs: A Social Security number (SSN) An Individual Taxpayer Identification Number (ITIN) An Employer Identification Number (EIN), also known as a FEIN (Federal Employer Identification Number) Less commonly used identification numbers are the Adoption taxpayer identification number (ATIN) and the Preparer tax identification number (PTIN)