In macroeconomics and modern monetary policy, a devaluation is an official lowering of the value of a country's currency within a fixed exchange-rate system, in which a monetary authority formally sets a lower exchange rate of the national currency in relation to a foreign reference currency or currency basket. The opposite of devaluation, a change in the exchange rate making the domestic currency more expensive, is called a revaluation. A monetary authority maintains a fixed value of its currency by being ready to buy or sell foreign currency with the domestic currency at a stated rate; a devaluation is an indication that the monetary authority will buy and sell foreign currency at a lower rate.