We develop a tractable dynamic model of productivity growth and technology spillovers that is consistent with the emergence of real world empirical productivity distributions. Firms can improve productivity by engaging in in-house R\&D, or alternatively, by trying to imitate other firms'...

This paper develops a fully-endogenous, variety-expansion growth model with firm-specific quality heterogeneity, limit pricing, and an endogenous distribution of markups. Trade induces only firms with high-quality products to export, whereas firms with low-quality products serve only the...