The objective of this paper is twofold. First, the paper develops a class of models of the term structure of interest rates, in the Heath, Jarrow, and Morton (1992) framework, with dynamics characterized by the evolution of a small set of state variables. Second, the paper exploits this characterization of the dynamics of the term structure in an estimation exercise that makes use of both the time series and cross-section of bond prices. In this way, our class of models bridges the gap between traditional models, such as Cox, Ingersoll, and Ross (1985) and Vasicek (1977), that emphasize the dynamics of interest rates and the models of Heath, Jarrow, and Morton (1992) that stress fitting the cross-section of bond prices.