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.
Download the W-9 Form here: http://www.irs.gov/pub/irs-pdf/fw9.pdf
Download the W-8 Form here: http://www.irs.gov/pub/irs-pdf/fw8ben.pdf