All foreign nationals present in the United States who have received income from a U.S. source are required by law to file Federal income tax returns with the U.S. Internal Revenue Service (IRS). When filing tax returns, most individuals use a Social Security Number (SSN) as the primary means of identification. For foreign nationals, however, who are not eligible for a SSN, an alternate identification number must be used in order to file their tax returns. This alternate identification number is called an Individual Taxpayer Identification Number (ITIN). If you do not meet the Social Security eligibility criteria you will need to apply for an ITIN.
It is important to note that if you first obtain an ITIN but later become eligible to receive an SSN, you must apply for an SSN and use your SSN in all future tax filings and documentation.