w-9 – A Form W-9 is a document issued by the United States Internal Revenue Service (IRS) for certain taxation purposes.w-8 – W8 is for non-US residents. For non-U.S residents who earned money from U.S based online affiliate programs, you will be asked to submit a W8 form.-9 – A Form W-9 is a document issued by the United States Internal Revenue Service (IRS) for certain taxation purposes.