We study the source of exchange rate fluctuations using a general equi-librium model accommodating shocks in goods and financial markets. These shocks differ in their induced comovements between exchange rates, interest rates, and quantities. A calibration matching data from the U.S. and G10 currency countries implies that persistent shocks to relative demand, reflected in persistent interest rate differentials, account for 75% of the variance in the dollar/G10 exchange rate. Shocks to currency intermediation are important, however, in generating deviations from uncovered interest parity at high fre-quencies and explaining the dollar appreciation in crises.