A Social Security Number (SSN) is a unique, 9-digit taxpayer identification number used for taxpayer identification, income reporting, and record-keeping purposes. The Social Security Administration (SSA) issues numbers to all U.S. citizens and permanent residents and to eligible foreign nationals. Eligibility to apply for a social security number is dependent on one's eligibility for employment in the U.S.

Everyone who is employed in the U.S. must have a social security number. Once issued, the number is valid for a lifetime. If you have been issued a number previously, do not apply for another as this will cause confusion in your tax records. If you do not have a social security number, you will need to visit one of the local Social Security Administration offices to apply for one.

Employers withhold social security tax, or FICA (Federal Insurance Contribution Act), from workers' wages for redistribution after retirement. In general, students and scholars in F-1 or J-1 status who are nonresidents for tax purposes do not have social security tax withheld. However, individuals filing as residents for tax purposes –dependents in J-2 status and scholars in H-1B, O-1, and TN status – do have social security tax withheld. F-1 and J-1 students generally are considered nonresidents for tax purposes for their first five years in the U.S. J-1 scholars are generally considered nonresidents for tax purposes for their first two years in the U.S.

The immigration status of all nonimmigrant applications for social security numbers must be verified by the Department of Homeland Security. Processing time for a social security number can take several weeks.

Individual Taxpayer Identification Number (ITIN)
Scholars who visit the university for nine days or less and receive honoraria or reimbursement do not need social security numbers. Instead, they will be asked by the university to complete, among other papers, a W-7 form to obtain an Individual Taxpayer Identification Number (ITIN) necessary to file their tax returns.

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