We thank Kala Krishna for encouraging us to write this paper. We benefited from comments by participants at the AEA Session on "Firm Heterogeneity and International Trade." All errors are our own. The views expressed herein are those of the author(s) and do not necessarily reflect the views of the National Bureau of Economic Research. NBER working papers are circulated for discussion and comment purposes. They have not been peerreviewed or been subject to the review by the NBER Board of Directors that accompanies official NBER publications.

This article looks at two features of globalization, namely, productivity improvements and falling trade costs, and explores their effect on welfare in a monopolistic competition model with heterogenous firms and technological asymmetries. Contrary to received wisdom, and for reasons different from adverse terms of trade effects, it is shown that improvements in a partner's productivity must hurt us. Moreover, falling trade costs can raise welfare in the technologically advanced country while reducing it in the backward one, if technological asymmetries are large enough.

In this paper we explore the effect of trade policy on productivity and welfare in the now standard model of firm-level heterogeneity and product differentiation with monopolistic competition. To obtain sharp results, we restrict attention to an economy that takes as given the price of imports and the demand schedules for its exports (a "small economy"). We first establish that welfare can be decomposed into four terms: productivity, terms of trade, variety and curvature, where the latter is a term that captures heterogeneity across varieties. We then show how a consumption subsidy, an export tax, or an import tariff allow our small economy to deal with two distortions that we identify and thereby reach its first best allocation. We also show that an export subsidy generates an increase in productivity, but given the negative joint effect on the other three terms (terms of trade, variety and curvature), welfare falls. In contrast, an import tariff improves welfare in spite of the fact that productivity falls.

This paper builds a tractable partial equilibrium model in the spirit of Melitz (2003), which incorporates two dimensions of heterogeneity: firms specific productivity shocks and firm-market specific demand shocks. The structural parameters of interest are estimated using only cross-sectional data, and counterfactual experiments regarding the effects of reducing costs, both fixed and marginal, or of trade preferences (with distortionary Rules of Origin) offered by an importing country are performed. Our counterfactuals make a case for "trade as aid" as such policies can create a ""win-win-win" scenario and are less subject to the usual worries regarding the efficacy of direct foreign aid. They also suggest that reducing fixed costs at various levels can be quite effective as export promotion devices, with the exports induced per dollar spent ranging from .4 to 25.

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