Form 6166 is the TRC for the United States, with the official IRS title being “Certification of US Tax Residency.” It is used by US residents to show foreign governments that they are eligible for tax treaty benefits. Example: A US resident who works as an engineer travels to Norway to work for a few weeks out of the year on a new pipeline. He was paid by a Norwegian company for work performed in Norway. To avoid being taxed at the higher rates in Norway and instead claim those wages in the US, he would need to present a US TRC: Form 6166. At doola, we can assist our customers with directly obtaining this form.