This paper develops an equilibrium model of the determination of exchange rates and prices of goods. Changes in relative prices due to supply or demand shifts induce changes in exchange rates and deviations from purchasing power parity. These changes may create a correlation between the exchange rate and the terms of trade, but this correlation cannot be exploited by governments to affect the terms of trade through foreign exchange market operations. The model emphasizes the role of relative price changes due to real disturbances and how these changes affect both exchange rates and the terms of trade through shifts in supply and demand. Government interventions in foreign exchange markets cannot influence exchange rates if the relationship between exchange rates and terms of trade is due to shifts in real supply and demand for domestic and foreign goods.