Separating trend from cycle is central to the study of long-run growth and the business cycle. The goal is to measure the permanent and transitory components of output to identify its long-run and business cycle fluctuations. In 1981, Beveridge and Nelson developed A New Approach to Permanent and Transitory Components with Particular Attention to Measurement of the “Business Cycle,” an econometric model that decomposes a time series into its permanent and transitory components. Much business cycle analysis of the last twenty-five years would not be possible without their decomposition.