U.S. beef cattle stocks are among the most periodic economic time series. A theory of cattle cycles is constructed on the basis of breeding stock inventory decisions. The low fertility rate of cows and substantial lags and future feedback between fertility and consumption decisions cause the demographic structure of the herd to respond cyclically to exogenous shocks in demand and production costs. Known demographic parameters of cattle imply sharp numerical benchmarks for the resulting dynamic system and closely compare with independent econometric time-series estimates over the 1875-1990 period. The model fits extremely well. Copyright 1994 by University of Chicago Press.