The new classical view that macroeconomic fluctuations can be modeled as an equilibrium system perturbed by transitory monetary disturbances has been challenged in recent years by another equilibrium view of fluctuations, the so-called real business cycle theory. In this latter framework, shocks to the production function induce both intertemporal substitution of labor supply and permanent shifts in the stochastic trend of output. Monetary shocks, on the other hand, play only a minor role in this view of the cycle. Much of the empirical support for the real business cycle view of fluctuations is based on a re-examination of traditional methods for detrending economic time series. The issues raised by the real business cycle theorists are not new; indeed, they go back at least to the NBER's first business cycle studies. However, the real business cycle theorists attach a radical economic interpretation to what, on the surface, appears to be a purely technical note on the proper method for detrending economic data. This paper reviews the debate over stochastic trends, discusses the economic implications of the real business cycle interpretation of stochastic trend models, and weighs the time series evidence for some of the stronger claims made by real business cycle theorists. We conclude that, while this literature raises real and useful questions about the interpretation of observed fluctuations, the new classical view of the cycle is not ruled out by the data.