If you ever received a paycheck, you know your employer takes out tax before the money hits your bank account. That is withholding — a system that collects tax at the source. In cross‑border payments, the same idea is the backbone of how governments make sure they actually get tax from people and companies that might not file a return. This chapter shows you how that administrative machinery works, from the basic 30% hit on a royalty payment to the global reporting net cast by FATCA.