You'll need an Individual Taxpayer Identification Number from the IRS – it's called ITIN for short – If you have a tax filing requirement, federal tax withholding or are eligible for an allowable tax benefit, but you aren't eligible for a Social Security number. Go to irs.gov/itin, where you can learn more about it. First, you'll complete a Form W-7. You'll mail this to the IRS along with the required identification documents and your federal tax return. Check out the instructions for Form W-7 for a list of acceptable documents. Only send original identification documents or a copy certified by the agency that issued it. You also have other options. Instead of mailing in original documents like your passport, you can work with a certifying acceptance agent. These agents are authorized by the IRS to authenticate your documents. Another option is to make an appointment to get help at an IRS Taxpayer Assistance Center that provides this service. Any ITIN not used on a tax return at least once in three years will expire at the end of the third year. If your ITIN expired and you need to file a tax return, be sure to also submit a completed Form W-7 and required documents to renew your expired ITIN. This helps avoid delays in the processing of your tax return and tax refund. Be sure to check that all other ITINs listed on your tax return haven't expired – like for your spouse or a dependent. For more information on ITINs and where you can get help, go to IRS.gov/itin.