Large-scale macroeconomic models have been used at the Federal Reserve Board for nearly 30 years. After briefly reviewing the first generation of Fed models, which were based on the IS/LM//Phillips curve paradigm, the paper describes the structure and properties of a new set of models. The new models are more explicit in their treatment of expectations formation and household and firm intertemporal decision-making. The incorporation of more rigorous theoretical microfoundations is accomplished while maintaining a high standard of goodness of fit. Simulations illustrate the effects of alternative assumptions about the formation of expectations and policy credibility on system properties.