FEDERAL DOCUMENTS

IRS Form 6166 (U.S. Residency Certification) Apostille

Form 6166 is the IRS letter certifying that a person or company is a U.S. resident for tax purposes. Foreign tax authorities, banks and paying agents often ask for it to apply treaty benefits, and many want it apostilled or legalized. Because it's a federal document, we route it to the U.S. Department of State and handle every step after that.

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FORM 6166

Authenticated for use abroad

For companies, funds and individuals.

Federal apostille, hand-carried in DC
Embassy legalization for non-Hague countries
Bundled with corporate documents
Tracked delivery worldwide

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What Form 6166 is used for

Form 6166 is issued by the IRS after you apply with Form 8802. It's often requested when a foreign country withholds tax on payments to U.S. residents, such as dividends, royalties, service fees or pensions, and a tax treaty may reduce that withholding. Some recipients accept the letter as is, while others want it apostilled or legalized. Ask the foreign payer or tax authority which they need.

Who we help

Companies receiving royalties or service fees from abroad
Life sciences and technology companies with foreign partners
Investment funds and their administrators
Individuals receiving foreign pensions or investment income
Accounting and tax firms handling clients' certifications
Law firms coordinating cross-border transactions

We handle authentication only. Tax questions belong with your tax advisor.

How it works

1
Send us the certification
The original Form 6166 issued by the IRS.
2
We confirm the route
Apostille for Hague countries, or authentication and embassy legalization for the rest.
3
Federal authentication
Our DC Satellite Office lets us hand-carry federal submissions to the U.S. Department of State, so your documents don't sit in the mail.
4
Shipped to you or abroad
To your office, your advisor or the foreign recipient.

Good to know

Check the tax year

Form 6166 covers specific tax years. Make sure yours matches what the recipient asks for.

Corporate packets

Often requested with a Certificate of Good Standing. See Good Standing.

Translation

Some countries want a translation. See Certified Translation.

Other federal records

See Federal Document Apostille.

Mistakes we help you avoid

The wrong tax year. Recipients often want the certification for a specific year.
Assuming the letter needs nothing more. Some recipients want it apostilled or legalized. Ask before the deadline.
Splitting a corporate packet. When several documents go to one country, we keep them together.
Sending to a state office. Form 6166 is federal and goes to the U.S. Department of State.

Official sources

We link to official sources so you can check the current rules yourself. Requirements change, and the receiving office always has the final word.

Frequently asked questions

Can a state apostille Form 6166?

No. It's issued by the IRS, a federal agency, so it's authenticated by the U.S. Department of State.

Do you apply for Form 6166 for me?

No. You or your tax advisor apply to the IRS. We authenticate the certification once it arrives.

Can you handle several certifications at once?

Yes. Companies often send multiple certifications for different countries.

Can you give tax advice?

No. Please speak with your tax advisor.

Do you invoice companies directly?

Yes, with an itemized invoice for each matter.

Need Form 6166 authenticated?

Tell us the country and the deadline.