On the international scene, away from national legal rules, the use of different currencies is largely due to the process of the ''''Invisible Hand''''. How do currencies flow when their circulations are not tightly guided and canalised? The paper develops a three-country model of the world economy and links real trade patterns with currency exchange structures in a general equilibrium framework which includes transaction costs on foreign exchange markets. It is shown that there are in general multiple equilibrium structures of currency exchange for a given underlying real trade pattern. The existence conditions of these different equilibria are characterized, using the trade links between countries as the key parameters. An evolutionary approach to equilibrium selection is used to explain the rise and fall of international currencies as the trade flows between the three economies are altered. Finally, repercussions of the choice of a currency exchange structure on welfare are analysed.
