This paper develops a multicountry model of international trade that provides a simple microfoundation for buyer-seller relationships in trade. We explore a rich data set that identifies buyers and sellers in trade and establish a set of basic facts that guide the development of the theoretical model. We use predictions of the model to examine the role of buyer heterogeneity in a market for firm-level adjustments to trade shocks, as well as to quantitatively evaluate how firms’ marginal costs depend on access to suppliers in foreign markets.

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.