A tax residency certificate is an official document issued by a country's tax authority confirming that a named individual, company or fund is resident there for tax purposes during a stated year or period. It is also called a certificate of residence or certificate of fiscal residence. Its main use is to prove to another country that the holder is covered by a double taxation treaty between the two states. In the United States the certificate is issued by the Internal Revenue Service as Form 6166.
Investors and businesses present the certificate to paying agents, custodians or foreign tax offices to obtain tax treaty relief, either as a lower rate of withholding tax when income is paid or as part of tax reclaim processing afterwards. Certificates are normally valid for a limited time. A certificate shows tax residency only; it does not prove that the holder is the beneficial owner of the income.