This paper presents a model of international trade that features heterogeneous firms, relative endowment differences across countries, and consumer taste for variety. The paper demonstrates that firm reactions to trade liberalization generate endogenous Ricardian productivity responses at the industry level that magnify countries' comparative advantage. Focusing on the wide range of firmlevel reactions to falling trade costs, the model also shows that, as trade costs fall, firms in comparative advantage industries are more likely to export, that relative firm size and the relative number of firms increases more in comparative advantage industries and that job turnover is higher in comparative advantage industries than in comparative disadvantage industries.

This paper examines the factors that give rise to intermediaries in exporting and explores the implications for trade volumes. Export intermediaries such as wholesalers serve different markets and export different products than manufacturing exporters do. Wholesalers are more prevalent in markets with higher destination-specific fixed costs and focus on products that are less differentiated, have lower contract intensity, and have large sunk entry costs. Aggregate exports to destinations with high shares of indirect exports are less responsive to changes in the real exchange rate than are exports to markets served primarily by direct exporters.

Research in international trade has changed dramatically over the last twenty years, as attention has shifted from countries and industries towards the firms actually engaged in international trade. The now-standard heterogeneous firm model posits measure-zero firms that compete under monopolistic competition and decide whether to export to foreign markets. However, much of international trade is dominated by a few “global firms,” which participate in the international economy along multiple margins and account for substantial shares of aggregate trade. We develop a new theoretical framework that allows firms to have large market shares and decide simultaneously on the set of production locations, export markets, input sources, products to export, and inputs to import. Using US firm and trade transactions data, we provide strong evidence in support of this framework's main predictions of interdependencies and complementarities between these margins of firm international participation. Global firms participate more intensively along each margin, magnifying the impact of underlying differences in firm characteristics and increasing their shares of aggregate trade.

Large multi-product firms dominate international trade flows. Using novel linked production and export data at the firm-product level, we find that the overwhelming majority of manufacturing firms export products that they do not produce. Three quarters of the exported products and 30% of export value from Belgian manufacturers are in goods that are not produced by the firm, so-called Carry-Along Trade (CAT). The number of CAT products is strongly increasing in firm productivity while the number of produced products that are exported is weakly increasing in firm productivity. We propose a general model of production and sourcing at multi-product firms and explore new demand- and supply-side modelling features capable of generating predictions consistent with the empirical findings. Export price data and company interviews offer suggestive evidence for the presence of demand-scope complementarities.

We explore firm size heterogeneity in production networks. In comprehensive data for Belgium, firms with more customers have higher total sales but lower sales and lower market shares per customer. Downstream factors, especially the number of customers, explain the vast majority of firm size dispersion. We rationalize these facts with a model of network formation and two-dimensional firm heterogeneity. Higher productivity generates more matches and larger market shares among customers. Higher relationship capability generates more customers and higher sales. Model estimates suggest a strong negative correlation between productivity and relationship capability and potentially large welfare gains from improving relationship capability.

Two identical firms who start exporting in different months, one each in January and December, will report dramatically different exports for the first calendar year. This partial-year effect biases down first-year export levels and biases up first-year export growth rates. For Peruvian exporters, the partial-year bias is large: first-year export levels are understated by 54 percent and the first-year growth rate is overstated by 112 percentage points. Correcting the partial-year effect dramatically reduces first-year export growth rates, raises initial export levels, and almost doubles the contribution of net firm entry and exit to overall export growth.

This paper examines the frequency, pervasiveness, and determinants of product switching by US manufacturing firms. We find that one-half of firms alter their mix of five-digit SIC products every five years, that product switching is correlated with both firm- and firm-product attributes, and that product adding and dropping induce large changes in firm scope. The behavior we observe is consistent with a natural generalization of existing theories of industry dynamics that incorporates endogenous product selection within firms. Our findings suggest that product switching contributes to a reallocation of resources within firms toward their most efficient use.

Intrafirm Trade and Product Contractibility by Andrew B. Bernard, J. Bradford Jensen, Stephen J. Redding and Peter K. Schott. Published in volume 100, issue 2, pages 444-48 of American Economic Review, May 2010

Wholesalers and Retailers in US Trade by Andrew B. Bernard, J. Bradford Jensen, Stephen J. Redding and Peter K. Schott. Published in volume 100, issue 2, pages 408-13 of American Economic Review, May 2010

Recent research in international trade emphasizes the importance of firms’ extensive margins for understanding overall patterns of trade as well as how firms respond to specific events such as trade liberalization. In this paper, we use detailed U.S. trade statistics to provide a broad overview of how the margins of trade contribute to variation in U.S. imports and exports across trading partners, types of trade (i.e. arm’s-length versus related-party) and both short and long time horizons. Among other results, we highlight the differential behaviour of related-party and arm’s-length trade in response to the 1997 Asian financial crisis.