A W-8 is a form required by the IRS (Internal Revenue Service) that foreign individuals and businesses must file to verify their country of residence for tax purposes. The W-8 form is required to be used by non-resident aliens or by foreign business entities who perform work and/or generate income in the U.S.
If you are a legal citizen of the United States, you will need to fill out the W-9 form. The W-8 tax form is only used by foreign persons or entities certifying their foreign status for tax purposes in the U.S.