The slope of the yield curve has been shown empirically to be a significant predictor of inflation and real economic activity but there is no standard theory as to why the relationship exists. This article constructs an analytical rational expectations model to investigate the reasons for the empirical results. The model suggests that the relationships are not structural but are instead influenced by the monetary policy regime. However, the yield curve should have predictive power for output and inflation in most circumstances. Various implications of the theoretical model are tested and confirmed empirically.