The IRS will issue an ITIN to an alien who does not have (and is not eligible to get) a social security number (SSN)  To apply for an ITIN, file Form W-7 Application for IRS Individual Taxpayer Identification Number, with the IRS.  It usually takes about 30 days to get an ITIN.  You would enter the ITIN whenever an SSN is required on a tax return.

Social Security Number (SSN)

Use your SSN as your taxpayer identification number.  You must put this number on each of your individual income tax forms, such as Form 1040 and all Schedules.

To apply for a SSN use Form SS-5, Application for a Social Security Card.  You can obtain this form from the Social Security Administration (SSA) offices or by calling 1 800-772-1213, or visit www.ssa.gov

Employer Identification Number (EIN)

You must have an EIN to use as a taxpayer identification number if you pay wages to one or more employees or file pension or excise tax returns.

You can get an EIN either through the mail or by telephone by filling out a Form SS-4, Application for Employer Identification Number.  This form is available from either the SSA or the IRS.