This paper examines the historical properties of business cycles across ten countries over the last century. It contrasts the properties of real quantities (such as output, consumption, investment, and net exports) with those of price levels and money stocks. While output fluctuations vary across countries and periods, the relationships among real quantities are remarkably uniform. Investment is consistently more volatile than output, and both are strongly procyclical. Consumption is about as volatile as output, and the trade balance is generally countercyclical. Government purchases, however, show no systematic cyclical tendency. Price level fluctuations have changed significantly over time. Before World War II, prices were predominantly procyclical, but since then they have been consistently countercyclical. Price level fluctuations have also been more persistent since World War II than in earlier periods. Money fluctuations are less highly correlated with output in the postwar period, but are no more persistent than in earlier periods. The study uses data from ten countries with at least a century of annual data on national output: Australia, Canada, Denmark, Germany, Italy, Japan, Norway, Sweden, the United Kingdom, and the United States. The data show that interwar fluctuations in real output are uniformly larger than those of the postwar period. However, there is no consistent pattern for the prewar/postwar comparison. In six of the ten countries, prewar fluctuations are no more than 60 percent larger than those of the postwar period. In the other four, prewar fluctuations are considerably larger. The study also examines the behavior of components of national output, including consumption, investment, government spending, and net exports. These components show similar patterns of procyclical behavior in the postwar period. Price level fluctuations have changed significantly over time, with price levels being more persistent since World War II than in earlier periods. The study also finds that the correlation between money and output has declined in the postwar period, but there is no general tendency for greater persistence of money growth rates. The study concludes that while prewar fluctuations were generally larger than those of the postwar period, the extent of the difference varies across countries. The interwar era experienced much larger fluctuations than the other two periods, although the extent of this extra volatility varies from country to country. The study also finds that the trade balance is generally countercyclical, with larger deficits during booms than recessions. The study provides evidence that the prewar period had more volatile output fluctuations than the postwar period, but the extent of this difference varies across countries. The study also finds that the correlation between price levels and output is positive in the prewar and interwar periods, but negative in the postwar period. The study concludes that the observed changes in price behavior are likely due to changes in the nature of economic fluctuations rather than measurement error.This paper examines the historical properties of business cycles across ten countries over the last century. It contrasts the properties of real quantities (such as output, consumption, investment, and net exports) with those of price levels and money stocks. While output fluctuations vary across countries and periods, the relationships among real quantities are remarkably uniform. Investment is consistently more volatile than output, and both are strongly procyclical. Consumption is about as volatile as output, and the trade balance is generally countercyclical. Government purchases, however, show no systematic cyclical tendency. Price level fluctuations have changed significantly over time. Before World War II, prices were predominantly procyclical, but since then they have been consistently countercyclical. Price level fluctuations have also been more persistent since World War II than in earlier periods. Money fluctuations are less highly correlated with output in the postwar period, but are no more persistent than in earlier periods. The study uses data from ten countries with at least a century of annual data on national output: Australia, Canada, Denmark, Germany, Italy, Japan, Norway, Sweden, the United Kingdom, and the United States. The data show that interwar fluctuations in real output are uniformly larger than those of the postwar period. However, there is no consistent pattern for the prewar/postwar comparison. In six of the ten countries, prewar fluctuations are no more than 60 percent larger than those of the postwar period. In the other four, prewar fluctuations are considerably larger. The study also examines the behavior of components of national output, including consumption, investment, government spending, and net exports. These components show similar patterns of procyclical behavior in the postwar period. Price level fluctuations have changed significantly over time, with price levels being more persistent since World War II than in earlier periods. The study also finds that the correlation between money and output has declined in the postwar period, but there is no general tendency for greater persistence of money growth rates. The study concludes that while prewar fluctuations were generally larger than those of the postwar period, the extent of the difference varies across countries. The interwar era experienced much larger fluctuations than the other two periods, although the extent of this extra volatility varies from country to country. The study also finds that the trade balance is generally countercyclical, with larger deficits during booms than recessions. The study provides evidence that the prewar period had more volatile output fluctuations than the postwar period, but the extent of this difference varies across countries. The study also finds that the correlation between price levels and output is positive in the prewar and interwar periods, but negative in the postwar period. The study concludes that the observed changes in price behavior are likely due to changes in the nature of economic fluctuations rather than measurement error.