Money does not stop at the border. Every time a country trades, invests, or borrows abroad, its currency meets another, and the rules that govern that meeting shape everything from the price of your morning coffee to whether a whole economy sinks into recession. In this chapter, we’ll see how those rules have changed over the last century and a half — from gold to dollars to floating rates — and what those changes meant for growth, inflation, and the freedom of governments to manage their own economies.