Since the advent of managed floating it has come to be accepted as a stylized fact that short-run deviations from purchasing power parity are both substantial and persistent. Two explanations of these deviations have been advanced in the literature. One emphasizes the role of changes in non-traded goods prices while the other views deviations from purchasing power parity as being due to sticky goods prices and slow adjustment of goods markets. This paper presents yet a third possible explanation of deviations from purchasing power parity - they may be necessary in order to facilitate the relative price changes that are required to maintain equilibrium in the face of unanticipated shocks. In addition, the issue of exchange rate overshooting is addressed. Whereas the sticky price models view exchange rate overshooting and exchange rate volatility as symptoms of some fundamental disequilibrium, the perspective taken here is that these events are, in principle, compatible with a world in which all markets clear continuously. © 1983.