Innovation, Firm Size Distribution, and Gains from Trade

We study a trade model with monopolistic competition a la Melitz (2003) that is standard except that firm heterogeneity is endogenously determined by firms innovating to enhance their productivities. We show that the equilibrium productivity and firm-size distributions exhibit power-law tails under rather general conditions on demand and technology. In particular, the emergence of the power laws is essentially independent of the underlying primitive heterogene-ity among firms. We investigate the model’s welfare implications, and conduct a quantitative analysis of welfare gains from trade. We find that, conditional on the same trade elasticity and values of the common parameters, our model yields 40% higher welfare gains from trade than a standard model with exogenously given productivity distribution.