A reserve currency is a foreign currency that a central bank or treasury holds as part of its country’s formal foreign exchange reserves. Countries hold reserves for a number of reasons, including to weather economic shocks, pay for imports, service debts, and moderate the value of its own currency. Many countries cannot borrow money or pay for foreign goods in their own currencies—since much of international trade is done in dollars—and therefore need to hold reserves to ensure a steady supply of imports during a crisis and assure creditors that debt payments denominated in foreign currency can be made.