Form 6166

Certification of US Tax Residency (Form 6166)

Form 6166 is a from the U.S Department of Treasury used as proof to foreign governments that U.S residents are eligible to receive tax treaty benefits. The United States has negotiated tax treaties with numerous countries worldwide that can help U.S residents and companies who do business abroad. Reduced tax rates, exemption from double taxation, and other significant benefits can apply to various forms of international income, including subscriptions, research payments, licensing / royalties etc.

Harvard University uses Form 6166 – Income Tax to claim income tax treaty and other tax benefits while doing business in foreign countries. Many U.S. tax treaty country partners require this proof of U.S. residency from the IRS when claiming income tax treaty benefits. Form 6166 - VAT is also used to claim exemption from a VAT (Value Added Tax) imposed by a foreign country.

In addition to the Forms 6166, country specific Forms may be required in Portugal Form 24-RFI and/or Form 21-RFI, Italy Form C, Indonesia DGT Form, or UK VAT66A.

The following countries require a country specific Form 6166 – Income Tax: Armenia, Azerbaijan, Belarus, Georgia, Greece, Kyrgyz Republic, Moldova, Portugal, Russia, Spain, Tajikistan, Turkmenistan, and Uzbekistan. All other countries take the “General” Form 6166.

If you need an original copy of Forms 6166, please contact Yvan Maniraguha Kywala at You can also find a copy of the Harvard University 2021 Forms 6166 Forms here