A certificate of coverage is an official form issued by the Social Security Administration (SSA) or an authorized agency of an agreement country to certify that the employee named on the form is subject to Social Security coverage in the issuing country and exempt from coverage in the other country.

Employees who are exempt from U.S. or foreign Social Security coverage under an agreement must document their exemption by obtaining a certificate of coverage from the country that will continue to cover them. For example, a U.S. worker sent on temporary assignment to the United Kingdom would need a certificate of coverage issued by SSA to prove the employee is covered by U.S. Social Security and exempt from U.K. Social Security taxes. Similarly, a U.K. national working temporarily in the United States would need a certificate issued by the U.K. Social Security authorities to prove the employee's 's exemption from U.S. Social Security tax.

A certificate of coverage issued by an agreement country serves as proof that the designated worker is exempt from U.S. Social Security coverage and taxes. If the worker is an employee, the foreign certificate should be retained in the office of the U.S. employer in case the Internal Revenue Service (IRS) questions why the company is not withholding and paying FICA taxes for the worker. If the worker is self-employed, a photocopy of the certificate must be attached to the U.S. income tax return the worker files each year to prove the employee's 's exemption from SECA taxes.

SSA sends duplicate copies of the certificates of coverage it issues on behalf of qualified U.S. employees to the requesting U.S. employers. It is the employers' responsibility to make a copy available to the tax authorities in the other country, if requested to do so, in order to prove the employee's 's foreign tax exemption.