Are you a U.S. citizen, a green card holder, or eligible for a Social Security Number (SSN)? If not, you will need to apply for an Individual Taxpayer Identification Number (ITIN) to meet your U.S. tax filing obligations. Non-resident aliens ineligible for an SSN must obtain an ITIN, as do spouses and dependents of U.S. citizens or green card holders who need to report income or meet tax requirements.