When and how do I apply for an Individual Taxpayer Identification Number (ITIN)?

You need an ITIN as soon as you are ready to file your federal income tax return, since you need to attach the return to your application.  To apply for an ITIN, complete Form W-7, Application for IRS Individual Taxpayer Identification Number.

There are exceptions to the requirement to include a U.S. tax return with the Form W-7. For example, if you are a nonresident alien individual eligible to get the benefit of reduced withholding under an income tax treaty, you can apply for an ITIN without having to attach a federal income tax return