Abstract Recent empirical evidence has highlighted how the export patterns of multi-product firms dominate world trade flows, and how these multi-product firms respond to different economic conditions across export markets by varying the number of products they export. In this paper, we further analyze the effects of those export market conditions on the relative export sales of those goods: we refer to this as the firm's product mix choice. We build a theoretical model of multi-product firms that highlights how market size and geography (the market sizes of and bilateral economic distances to trading partners) affects both a firm's exported product range and its exported product mix across market destinations. We show how tougher competition in an export market -associated with a downward shift in the distribution of markups across all products sold in the 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. Our theoretical model shows how this effect of export market c o m p e t i t i o n o n a f i r m ' s p r o d u c t m i x t h e n t r a n s l a t e s i n t o d i f f e r e n c e s i n m e a s u r e d f i r m productivity. Thus, a firm operating a given technology will produce relatively more output per worker when it exports to markets with tougher competition. This productivity gain is further compounded by the effect of competition on the mix of exported products. ____________________________ *We thank Steve Redding for helpful comments and suggestions. Ottaviano thanks MIUR and the European Commission for financial support. Melitz thanks the Sloan Foundation for financial support.

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Standard-Nutzungsbedingungen: Die Dokumente auf EconStor dürfen zu eigenen wissenschaftlichen Zwecken und zum Privatgebrauch gespeichert und kopiert werden. Sie dürfen die Dokumente nicht für öffentliche oder kommerzielle Zwecke vervielfältigen, öffentlich ausstellen, öffentlich zugänglich machen, vertreiben oder anderweitig nutzen. Sofern die Verfasser die Dokumente unter Open-Content-Lizenzen (insbesondere CC-Lizenzen) zur Verfügung gestellt haben sollten, gelten abweichend von diesen Nutzungsbedingungen die in der dort genannten Lizenz gewährten Nutzungsrechte. Terms of use: Documents in Statement of purpose: The purpose of these working papers is to promote the circulation of research results (Research Series) and analytical studies (Documents Series) made within the National Bank of Belgium or presented by external economists in seminars, conferences and conventions organised by the Bank. The aim is therefore to provide a platform for discussion. The opinions expressed are strictly those of the authors and do not necessarily reflect the views of the National Bank of Belgium. Orders For orders and information on subscriptions and reductions: National Bank of Belgium, Documentation -Publications service, boulevard de Berlaimont 14, 1000 Brussels. Abstract Secondary markets for long-term assets might be illiquid due to adverse selection. In a model in which moral hazard is confined to project initiation, I find that: (1) when agents expect a liquidity dryup on such markets, they optimally choose to self-insure through the hoarding of non-productive but liquid assets; (2) such a response has negative externalities as it reduces ex-post market participation, which worsens adverse selection and dries up market liquidity; (3) liquidity dry-ups are Pareto inefficient equilibria; (4) the Government can rule them out. Additionally, when agents face idiosyncratic, privately known, illiquidity shocks, I show that: (5) it increases market liquidity;

Standard-Nutzungsbedingungen: Die Dokumente auf EconStor dürfen zu eigenen wissenschaftlichen Zwecken und zum Privatgebrauch gespeichert und kopiert werden. Sie dürfen die Dokumente nicht für öffentliche oder kommerzielle Zwecke vervielfältigen, öffentlich ausstellen, öffentlich zugänglich machen, vertreiben oder anderweitig nutzen. Sofern die Verfasser die Dokumente unter Open-Content-Lizenzen (insbesondere CC-Lizenzen) zur Verfügung gestellt haben sollten, gelten abweichend von diesen Nutzungsbedingungen die in der dort genannten Lizenz gewährten Nutzungsrechte. Terms of use: Documents in Statement of purpose: The purpose of these working papers is to promote the circulation of research results (Research Series) and analytical studies (Documents Series) made within the National Bank of Belgium or presented by external economists in seminars, conferences and conventions organised by the Bank. The aim is therefore to provide a platform for discussion. The opinions expressed are strictly those of the authors and do not necessarily reflect the views of the National Bank of Belgium. Orders Abstract The paper describes job flows in Belgium using micro data at the firm level collected through the annual social balance sheets that companies have to file with the National Bank of Belgium. The coverage of the study is very broad: all industries and commercial services are included. We contribute to the previous literature by studying a long period from 1998 to 2006, covering both upturns and downturns in the Belgian economy. Furthermore, data from the social balance sheets make it possible to take into account the heterogeneity of the workforce, on top of the heterogeneity of firms themselves: job flows are broken down by socio-professional status and type of employment contract. JEL-code : J23, J21, I20.

Standard-Nutzungsbedingungen: Die Dokumente auf EconStor dürfen zu eigenen wissenschaftlichen Zwecken und zum Privatgebrauch gespeichert und kopiert werden. Sie dürfen die Dokumente nicht für öffentliche oder kommerzielle Zwecke vervielfältigen, öffentlich ausstellen, öffentlich zugänglich machen, vertreiben oder anderweitig nutzen. Sofern die Verfasser die Dokumente unter Open-Content-Lizenzen (insbesondere CC-Lizenzen) zur Verfügung gestellt haben sollten, gelten abweichend von diesen Nutzungsbedingungen die in der dort genannten Lizenz gewährten Nutzungsrechte. Papers presented at this colloquium are made available to a broader audience in the NBB Working Paper Series (www.nbb.be). Terms of use: Documents in Statement of purpose: The purpose of these working papers is to promote the circulation of research results (Research Series) and analytical studies (Documents Series) made within the National Bank of Belgium or presented by external economists in seminars, conferences and conventions organised by the Bank. The aim is therefore to provide a platform for discussion. The opinions expressed are strictly those of the authors and do not necessarily reflect the views of the National Bank of Belgium. Orders For orders and information on subscriptions and reductions: National Bank of Belgium, Documentation -Publications service, boulevard de Berlaimont 14, 1000 Brussels. Tel +32 2 221 20 33 -Fax +32 2 21 30 42 The Working Papers are available on the website of the Bank: http://www.nbb.be. vision about the working of the market system and as a conceptual apparatus. Particular attention is given to the contrast between Keynesian and Lucasian macroeconomics. The paper ends with a few remarks about the impact of the present crisis on the development of macroeconomic theory.