This thesis consists of four essays, covering four different topics. The first essay investigates the relationship between inter-firm labor mobility and regional productivity growth. Previous studies have shown that density is positively correlated with growth. I claim that it is not density in itself, but rather the attributes associated with it that drives economic growth. One such attribute is the increased possibility for labor mobility and knowledge diffusion that follows when firms and individuals locate in close proximity to each other. This hypothesis is tested using density as an instrument for labor mobility. The result shows that labor mobility increases regional growth rates. The second essay examines the relationship between agglomeration economies and relative wage costs in influencing location of multinational corporations. An inflow of firms to certain regions and industries is likely to increase demand for labor. If mobility of labor is low increased costs can be expected to deter additional inflows of firms, albeit agglomeration economies may compensate for higher wages. The empirical analysis finds that FDI has become increasingly sensitive to differences in wage costs across industrialized countries, but also that agglomeration economies related to knowledge externalities positively influences higher costs. The third essay looks at the impact of FDI on home country investments. Previous research has been inconclusive as regards the effects on domestic investments. In this article, we show that this inconclusiveness can be explained at a disaggregated level as a function of the way industries are organized. We argue that a complementary relationship can be expected to prevail in vertically integrated industries, whereas a substitutionary relationship can be expected in horizontally organized production. The empirical analysis confirms a significant difference between the two categories of industry as regards the impact of outward FDI on domestic investment. The fourth, and final, essay of this thesis analyses how increased R&D expenditures and market size influence the distribution of comparative advantage. Previous studies report ambiguous results and also refer to periods when markets were much more segmented and production factors less mobile. The empirical analysis comprises 19 OECD-countries and spans the period 1981 to 1999. It is shown how an increase in R&D-expenditures by one percentage point implies a three-percentage point increase in high-technology exports, whereas market size fails to attain significance. In addition, institutional factors influence the dynamics of comparative advantage.