Do you have citizenship in the United States? Are you a green-card holder? Do you have a Social Security number, or do you qualify to get one? If the answer is no, then you must apply for an ITIN number to file your taxes in the US. Non-resident aliens who do not qualify for an SSN need to apply for an ITIN number. Spouses and dependents of US citizens, and green card holders are also eligible for the identification number.