ITG FAQ #5 Answer-What is a Form W-9 and when is it applicable?
Form W-9, Request for Taxpayer Identification Number and Certification, is used by a U.S. person (including a resident alien) to give their correct TIN to the person requesting it, and when applicable, to:
certify the TIN you are giving is correct (or you are waiting for a number to be issued),
certify you are not subject to backup withholding, or
claim exemption from backup withholding if you are an exempt payee.