IRS Form W-8BEN is used to certify your status as a non-U.S. taxpayer. It is also used to claim reduced tax withholding on dividends and other income paid with respect to U.S. securities, where available. You need to have a valid W-8BEN form in order to trade in U.S. markets. It has a validity of 3 years and clients are required to resubmit after the 3rd calendar year.