The widespread tendency in empirical studies of economic behavior to discard war years as "abnormal," while doubtless often justified, is, on the whole, unfortunate. The major defect of the data on which economists must rely on is that the data generated by experience rather than deliberately contrived experiment, encompasses a small range of variation. Experience in general proceeds smoothly and continuously. In consequence, it is difficult to disentangle systematic effects from random variation since both are of much the same order of magnitude. From this point of view, data for wartime periods are peculiarly valuable. At such times, violent changes in major economic magnitudes occur over relatively brief periods, thereby providing precisely the kind of evidence that we would like get by "critical" experiments if we could conduct them. Of course, the source of changes means that effects in which we are interested are necessarily intertwined with others that we would eliminate from a contrived experiment. But this difficulty applies to all our data, not to data for wartime periods alone. To the student of monetary phenomena, the three wartime episodes with which this paper deals the experience of the United States in the Civil War, first World War and second World War offer an especially close approximation to the kind of critical experiment he would like to conduct. As we shall see, in all three cases the rise in prices was of almost precisely the same magnitude, so this critical variable is under control. Yet other crucial features varied, offering the opportunity to test alternative hypotheses designed to explain price changes. Besides their significance for the general understanding of monetary phenomena, the wartime experiences are unfortunately of interest in their own right.