The possibilities for types of taxpayer ID numbers include:
- Social Security number (SSN). A social security number is the most common identifier for personal identification and tax purposes.
- Employer ID number. An Employer ID (or EIN, for short) is a federal tax identification number for businesses. Although it's labeled as an identifier for "employers," you don't have to have employees to need an EIN.
- Individual Taxpayer ID number (ITIN)