The W-8BEN advises a United States customer of a foreign supplier that the supplier is not liable to taxation in the United States.
Liability to taxation in the United States is determinable under the Internal Revenue Code and also the treaty.
The W-8BEN is one of a series of three forms that may apply in the circumstances, W-8ECI and W-9 are alternative forms which may be appropriate in the situation where it has been determined that there is a United States tax liability.