This paper surveys the field of asset pricing. The emphasis is on the interplay between theory and empirical work and on the trade‐off between risk and return. Modern research seeks to understand the behavior of the stochastic discount factor (SDF) that prices all assets in the economy. The behavior of the term structure of real interest rates restricts the conditional mean of the SDF, whereas patterns of risk premia restrict its conditional volatility and factor structure. Stylized facts about interest rates, aggregate stock prices, and cross‐sectional patterns in stock returns have stimulated new research on optimal portfolio choice, intertemporal equilibrium models, and behavioral finance.

We show that the external habit‐formation model economy of Campbell and Cochrane (1999) can explain why the Capital Asset Pricing Model (CAPM) and its extensions are betterapproximate asset pricing models than is the standard onsumption‐based model. The model economy produces time‐varying expected eturns, tracked by the dividend–price ratio. Portfolio‐based models capture some of this variation in state variables, which a state‐independent function of consumption cannot capture. Therefore, though the consumption‐based model and CAPM are both perfect conditional asset pricing models, the portfolio‐based models are better approximate unconditional asset pricing models.