We develop a monopolistically competitive model of trade with firm heterogeneity -in terms of productivity differences -and endogenous differences in the 'toughness' of competition across markets -in terms of the number and average productivity of competing firms. We analyze how these features vary across markets of different size that are not perfectly integrated through trade; we then study the effects of different trade liberalization policies. In our model, market size and trade affect the toughness of competition, which then feeds back into the selection of heterogeneous producers and exporters in that market. Aggregate productivity and average markups thus respond to both the size of a market and the extent of its integration through trade (larger, more integrated markets exhibit higher productivity and lower markups). Our model remains highly tractable, even when extended to a general framework with multiple asymmetric countries integrated to different extents through asymmetric trade costs. We believe this provides a useful modeling framework that is particularly well suited to the analysis of trade and regional integration policy scenarios in an environment with heterogeneous firms and endogenous markups.

We build a theoretical model of multi-product firms that highlights how competition across market destinations affects both a firm’s exported product range and product mix. We show how tougher competition in an export market induces a firm to skew its export sales toward its best performing products. We find very strong confirmation of this competitive effect for French exporters across export market destinations. Theoretically, this within-firm change in product mix driven by the trading environment has important repercussions on firm productivity. A calibrated fit to our theoretical model reveals that these productivity effects are potentially quite large.

We model an OLG economy where productivity growth comes from two alternative sources: process innovation and learning-by-doing. There is a trade-off between the two in so far as frequent technological updates reduce the scope for learning on existing technologies. A conflict is shown to arise between the young and the old, because the former favor innovation while the latter prefer learning. We model the interaction between different generations and short-lived policy makers as a dynamic common agency problem, where competing generations invest a certain amount of resources to lobby either for the maintainance of the current technology or the adoption of a new one. By focusing on truthful Markov perfect equilibria, we characterize the political equilibrium and show its dependence on the underlying technological parameters.

We provide novel insights on the decentralization of optimal outcomes under monopolistic competition with nonseparable utility, variable demand elasticity, and endogenous firm heterogeneity. Relative to the unconstrained optimum, equilibrium firm selection is too weak, average firm size is too small, low-cost firms are too small, and high-cost firms are too large. The unconstrained optimum can be decentralized through differentiated production subsidies to producers financed through lump-sum taxes on entrants and consumers. When differentiated subsidies and transfers from entrants are not viable, the constrained optimum can be decentralized through a common production subsidy financed by a lump-sum tax on consumers.

We document how demand shocks in export markets lead French multiproduct exporters to reallocate the mix of products sold in those destinations. In response to positive demand shocks, French firms skew their export sales toward their best-performing products. We develop a theoretical model of multiproduct firms and derive the specific demand conditions (with endogenous price elasticities) needed to generate these product-mix reallocations. Under those demand conditions, the increased competition from demand shocks in export markets also induces productivity changes within the firm. We empirically test for this connection between demand shocks and the productivity of multiproduct firms. We find that this connection is economically substantial.

Following Grossman and Rossi-Hansberg (2008) we present a model in which tasks of varying complexity are matched to workers of varying skill in order to develop and test predictions regarding the effects of immigration and offshoring on US native-born workers. We find that immigrant and native-born workers do not compete much due to the fact that they tend to perform tasks at opposite ends of the task complexity spectrum, with offshore workers performing the tasks in the middle. An effect of offshoring and a positive effect of immigration on native-born employment suggest that immigration and offshoring improve industry efficiency.