What document can you present to confirm that you are a U.S. resident for tax purposes?

Form 6166 (U.S. Residency Certification)

Many U.S. treaty partners require the IRS to certify that the company claiming treaty benefits is a resident of the United States for the federal tax purposes. The IRS provides this residency certification on Form 6166, a letter of U.S. residency certification.

* DESCRIPTION: Form 6166 is a letter printed on U.S. Department of Treasury stationary certifying that the company or an individual was/is a resident of the United States for purposes of income tax laws of the United States. You may use this form to claim income tax treaty benefits and certain other tax benefits in foreign countries. Form 6166 also sets forth the Employer Identification Number (EIN) of the company of Social Security Number of the individula person, and the tax year the letter is issued for.
* RETRIEVAL: Upon request the IRS will issue original Form 6166 as conclusive evidence that you or your company is/was a U.S. resident for purposes of U.S. taxation. The process of obtaining the original Form 6166 from the IRS is called the “retrieval”. The original Form 6166 bears the Seal of the Internal Revenue Service, the signature of the Field Director State, and is printed on the watermarked green paper with many security features.
* LEGALIZATION: APOSTILLE: If the document is intended for use in a foreign country it has to be legalized (another word is “authenticated”) for foreign use. This is a process in which various seals are placed on the document. The legalization procedure basically depends on one factor: whether the target country has joined the Convention Abolishing the Requirement of Legalization for Foreign Public Documents (“The Hague Convention”). In this case the only legalization required is an Apostille certificate. (Apostille is a French word which means a certification). A document bearing an Apostille is valid in all of the Hague countries .
* CONSULAR LEGLAIZATION: Many foreign jurisdictions have not joined the Hague Convention. If the document is intended for a non-Hague country the consular legalization will be required. Before the consulate or the embassy can stamp the document, the document has to be authenticated on the state and federal levels.
* LEGALIZATION REQUIREMENTS: Form 6166 is a federal document therefore it has to be legalized on a federal level. Only original documents can be accepted for legalization. Notarized copies are not accepted.