To file a return electronically, the IRS requires a Social Security Number (SSN) or an Individual Taxpayer Identification Number (ITIN) for each person(s) listed on your return. If you, your dependent(s) or spouse does not have (and is not eligible to receive) a SSN, then you must list the ITIN instead of a SSN. The ITIN would have been issued by the IRS. See this article from the IRS for more info https://www.irs.gov/credits-deductions/individuals/how-do-i-apply-for-an-itin