This paper reviews the new approach to international trade based on firm heterogeneity in differentiated product markets. This approach explains a variety of features exhibited in disaggregated trade data, including the higher productivity of exporters relative to non-exporters, within-industry reallocations of resources following trade liberalization, and patterns of trade participation across firms and destination markets. Accounting for these empirical patterns reveals new mechanisms through which the aggregate economy is affected by trade liberalization, including endogenous increases in average industry and firm productivity.

In this paper, we analyze the transition dynamics associated with an economy's response to trade liberalization. We start by reviewing the recent literature that incorporates firm dynamics into models of international trade. We then build upon that literature to characterize the role of firm dynamics, export-market selection, firm-level innovation, sunk export costs, and firms' expectations regarding the time path of liberalization in generating those transition dynamics following trade liberalization. These modeling ingredients generate substantial aggregate transition dynamics as they shift and shape the endogenous distribution of firms over time. Our results show how the responses of trade volumes, innovation, and aggregate output can vary greatly over time depending on those modeling ingredients. This has important consequences for many issues in international economics that rely on predictions for the effects of globalization over time on those key aggregate outcomes.  

We examine how firm heterogeneity influences aggregate welfare through endogenous firm selection. We consider a homogeneous firm model that is a special case of a heterogeneous firm model with a degenerate productivity distribution. Keeping all structural parameters besides the productivity distribution the same, we show that the two models have different aggregate welfare implications, with larger welfare gains from reductions in trade costs in the heterogeneous firm model. Calibrating parameters to key U.S. aggregate and firm statistics, we find these differences in aggregate welfare to be quantitatively important (up to a few percentage points of GDP). Under the assumption of a Pareto productivity distribution, the two models can be calibrated to the same observed trade share, trade elasticity with respect to variable trade costs, and hence welfare gains from trade (as shown by Arkolakis, Costinot and Rodriguez-Clare, 2012); but this requires assuming different elasticities of substitution between varieties and different fixed and variable trade costs across the two models.

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 towards 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.

The rising prominence of intra-industry trade and huge multinationals has transformed the way economists think about the gains from trade. In the past, we focused on gains that stemmed either from endowment differences (wheat for iron ore) or inter-industry comparative advantage (David Ricardo's classic example of cloth for port). Today, we focus on three sources of gains from trade: 1) love-of-variety gains associated with intra-industry trade; 2) allocative efficiency gains associated with shifting labor and capital out of small, less-productive firms and into large, more-productive firms; and 3) productive efficiency gains associated with trade-induced innovation. This paper reviews these three sources of gains from trade both theoretically and empirically. Our empirical evidence will be centered on the experience of Canada following its closer economic integration in 1989 with the United States—the largest example of bilateral intra-industry trade in the world—but we will also describe evidence for other countries.

We extend the theoretical framework in Cuñat and Melitz (2007) to a many-country setup where countries exhibit different degrees of labor market flexibility. We rely on the insights from a recent paper by Costinot (2009) to obtain precise predictions about comparative advantage in this setting: countries with more flexible labor markets specialize in more volatile industries.

We develop a simple model of international trade with heterogeneous firms that is consistent with a number of stylized features of the data. In particular, the model predicts positive as well as zero trade flows across pairs of countries, and it allows the number of exporting firms to vary across destination countries. As a result, the impact of trade frictions on trade flows can be decomposed into the intensive and extensive margins, where the former refers to the trade volume per exporter and the latter refers to the number of exporters. This model yields a generalized gravity equation that accounts for the self-selection of firms into export markets and their impact on trade volumes. We then develop a two-stage estimation procedure that uses an equation for selection into trade partners in the first stage and a trade flow equation in the second. We implement this procedure parametrically, semiparametrically, and nonparametrically, showing that in all three cases the estimated effects of trade frictions are similar. Importantly, our method provides estimates of the intensive and extensive margins of trade. We show that traditional estimates are biased and that most of the bias is due not to selection but rather due to the omission of the extensive margin. Moreover, the effect of the number of exporting firms varies across country pairs according to their characteristics. This variation is large and particularly so for trade between developed and less developed countries and between pairs of less developed countries.

Empirical studies of production units within sectors have reported a massive amount of heterogeneity in various performance measures (most notably, size and productivity). This heterogeneity, within sectors, matters for theoretical and empirical models of trade. Trade, or trade liberalization more generally, induces important reallocations between heterogeneous producers in a sector: the smallest or least productive producers are forced to exit, and market shares are further reallocated between less productive producers (who do not export) towards larger, more productive exporters. These reallocations generate a new channel for productivity and welfare gains from trade.

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 analyse 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 mark-ups 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 mark-ups). 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 modelling framework that is particularly well suited to the analysis of trade and regional integration policy scenarios in an environment with heterogeneous firms and endogenous mark-ups.

We build a dynamic model of …rm-level adjustment to trade liberalization that jointly in- corporates the main salient features highlighted by recent empirical micro-level studies of …rms and trade. Our model captures the joint entry, exit, export, and innovation decisions (subject to sunk costs) of heterogeneous …rms as they adjust to trade liberalization. We characterize this industrial evolution over its entire transition path to a new steady state with lower trade costs - starting from the time that trade liberalization is …rst announced (but not necessarily yet implemented). We rely on numerical methods to solve for these equilibrium paths. In order to more accurately capture the dynamics of …rm adjustments to trade, we model the sunk nature of market entry costs for both the domestic and export market - as well as the per-unit and additional …xed costs of exporting incurred in every period. Firm-level productivity evolves stochastically, and innovation involves a trade-o¤ between its cost and a return in terms of a “better”distribution of future productivity draws. Although the empirical micro-level studies of …rms and export status initially emphasized the selection e¤ects of more productive …rms into export markets, several recent studies have highlighted a separate channel for the e¤ects of trade on productivity operating through …rm- level improvements in productivity. Our model captures both of these channels for the pro- ductivity enhancing e¤ects of trade - and analyzes their interactions over the adjustment path to lower trade costs. In particular, we highlight how the relative timing and magnitude of …rm-level productivity improvements and export market entry decisions are also determined by non-technological factors such as the timing of trade liberalization announcements and the speed of liberalization. Under all these di¤erent trade liberalization scenarios (anticipated ver- sus surprise, gradual versus sudden), we characterize both the distributional e¤ects across …rms as well as their aggregate e¤ects for industrial performance. We …nd that the anticipation of upcoming liberalization, and a more gradual path of liberalization (once implemented) induces …rms to innovate ahead of export market entry.

This paper studies the role of endogenous producer entry and product creation for monetary policy analysis and business cycle dynamics in a general equilibrium model with imperfect price adjustment. Optimal monetary policy stabilizes product prices, but lets the consumer price index vary to accommodate changes in the number of available products. The free entry condition links the price of equity (the value of products) with marginal cost and markups, and hence with inflation dynamics. No-arbitrage between bonds and equity links the expected return on shares, and thus the financing of product creation, with the return on bonds, affected by monetary policy via interest rate setting. This new channel of monetary policy transmission through asset prices restores the Taylor Principle in the presence of capital accumulation (in the form of new production lines) and forward-looking interest rate setting, unlike in models with traditional physical capital. We also study the implications of endogenous variety for the New Keynesian Phillips curve and business cycle dynamics more generally, and we document the effects of technology, deregulation, and monetary policy shocks, as well as the second moment properties of our model, by means of numerical examples.

We use a two-country, stochastic, general equilibrium model of international trade and macro- economic dynamics with monopolistic competition and heterogeneous …rms to explore the role of entry in the domestic economy and the extensive margin of international trade in the dynamics of U.S. trade ‡ows over the business cycle. We show that the model can reproduce the evidence on the cyclicality of U.S. trade and important features of the evidence on the extensive margins of domestic entry and international trade. Entry in the domestic economy and the implied di¤erences in the timing of export and import expansions in response to favorable productivity shocks provide the key mechanism for the model’s ability to explain this range of stylized facts.

We study the e¢ ciency properties of a dynamic, stochastic, general equilibrium, macroeco- nomic model with monopolistic competition and …rm entry subject to sunk costs, a time-to-build lag, and exogenous risk of …rm destruction. Under inelastic labor supply and linearity of produc- tion in labor, the market economy is e¢ cient if and only if symmetric, homothetic preferences are of the C.E.S. form studied by Dixit and Stiglitz (1977). Otherwise, e¢ ciency is restored by properly designed sales, entry, or asset trade subsidies (or taxes) that induce markup synchro- nization across time and states, and align the consumer surplus and pro…t destruction e¤ects of …rm entry. When labor supply is elastic, heterogeneity in markups across consumption and leisure introduces an additional distortion. E¢ ciency is then restored by subsidizing labor at a rate equal to the markup in the market for goods. Our results highlight the importance of preserving the optimal amount of monopoly pro…ts in economies in which …rm entry is costly. Inducing marginal cost pricing restores e¢ ciency only when the required sales subsidies are …nanced with the optimal split of lump-sum taxation between households and …rms.

We develop a stochastic, general equilibrium, two-country model of trade and macroeconomic dynamics. Productivity differs across individual, monopolistically competitive firms in each country. Firms face a sunk entry cost in the domestic market and both fixed and per-unit export costs. Only relatively more productive firms export. Exogenous shocks to aggregate productivity and entry or trade costs induce firms to enter and exit both their domestic and export markets, thus altering the composition of consumption baskets across countries over time. In a world of flexible prices, our model generates endogenously persistent deviations from PPP that would not exist absent our microeconomic structure with heterogeneous firms. It provides an endogenous, microfounded explanation for a Harrod- Balassa-Samuelson effect in response to aggregate productivity differentials and deregulation. Finally, the model successfully matches several moments of U. S. and international business cycles.

This paper develops and analyzes a welfare maximizing model of infant industry protection. The domestic infant industry is competitive and experiences dynamic learning effects that are external to firms. The competitive foreign industry is mature and produces a good that is an imperfect substitute for the domestic good. A government planner can protect the infant industry using domestic production subsidies, tariffs, or quotas in order to maximize domestic welfare over time. As protection is not always optimal (although the domestic industry experiences a learning externality), the paper shows how the decision to protect the industry should depend on the industry’s learning potential, the shape of the learning curve, and the degree of substitutability between domestic and foreign goods. Assuming some reasonable restrictions on the flexibility over time of the policy instruments, the paper subsequently compares the effectiveness of the different instruments. Given such restrictions, the paper shows that quotas induce higher welfare levels than tariffs. In some cases, the dominance of the quota is so pronounced that it compensates for any amount of government revenue loss related to the administration of the quota (including the case of a voluntary export restraint, where no revenue is collected). In similar cases, the quota may even be preferred to a domestic production subsidy.