The Internal Revenue Service issues several different types of tax identification numbers depending on the person or entity applying. Most U.S. citizens use their social security numbers for tax identification. Most non-citizens must contact the IRS to obtain an individual ID.
Businesses and nonprofit organizations are assigned an Employee Identification Number, which can be acquired instantly online at the IRS website. Individual Taxpayer Identification Numbers are issued to resident or nonresident aliens without social security numbers. Apply for these using Form W-7, available on the IRS website. Adoption Taxpayer Identification Numbers are assigned by the IRS as temporary ID for adopted children without social security numbers. Additionally, tax preparers must obtain a Paid Preparer Tax Identification Number to identify themselves on clients' tax forms.