We develop a model of firm dynamics through product innovation that explicitly incorporates advertising decisions by firms. We model advertising by constructing a framework that unifies a number of facts identified by the empirical marketing literature. The model is then used to explain several empirical regularities across firm sizes using U.S. data. Through a novel interaction between R&D and advertising, we are able to explain empirically observed deviations from Gibrat's law, as well as the behavior of advertising expenditures across firms, the degree of substitution between R&D and advertising expenditures as firms grow large, and broadly the effects of advertising on both firm and economic growth. We find that smaller firms can be both more innovation-and advertising-intensive as in the data even when there exist increasing returns to scale in research.

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This paper analyzes the implications of advertising for firm dynamics and economic growth through its interaction with R&D. We develop a model of endogenous growth with firm heterogeneity that incorporates advertising decisions and calibrate it to match several empirical regularities across firm size. Our model provides microfoundations for the empirically observed negative relationship between both firm R&D intensity and growth and firm size. In the calibrated model, about half of the deviation from proportional firm growth is attributed to our novel advertising channel. In addition, R&D and advertising are substitutes, a prediction for which we find evidence in the data. (JEL D22, E23, H25, L25, M37, O32)