A disproportionate share of world exports are also invoiced in dollars. That's partly because widespread demand for dollar assets makes borrowing in dollars slightly cheaper than alternatives — and invoicing increases the demand for those assets 7/

Getting a bit more specific: Money fills three roles: medium of exchange, store of value, unit of account. The dollar is to other moneys as money is to goods, with the added dimension that these roles involve both private-sector decisions and those of governments. I use the following table 4/