The contents of this manuscript were delivered as the Zeuthen Lectures on April 25 to 27, 2007, at the University of Copenhagen. I would like to thank Karl Gunnar Persson for the generous invitation to present these lectures, along with his colleagues at the Department of Economics for their hospitality. These lectures were also presented at the University of Nottingham on April 14 to 16, 2008. The comments of participants at both locations have benefited the research discussed here. In preparing this manuscript, I have received invaluable assistance from Hong Ma, now at Tsinghua University, to whom I am most grateful.
Some time as passed since the lectures were given, so it is inevitable that the ideas have been further developed and benefited from closely related publications. In particular, portions of chapter2 in this manuscript are drawn from Feenstra (2006) in the Review of World Economics/Weltwirtschaftliches Archiv (Springer) and Feenstra (1994) in the American Economic Review; portions of chapter3 are drawn from Feenstra (2010) in the Canadian Journal of Economics (Blackwell Publishing); portions of chapter4 are drawn from Feenstra and Kee (2008) in the Journal of International Economics (Elsevier); and portions of chapters5 and 6 are drawn from Feenstra, Heston, Timmer, and Deng (2009) in the Review of Economics and Statistics ( MIT Press). It is hoped that by integrating the material from these various sources into this manuscript I will have achieved more than the sum of the parts: that as a result, the contribution of import and export variety to the gains from trade will be more apparent, as well as directions for further research. (p.x)