This dissertation consists of three essays in international trade. The first chapter analyzes integration strategies of Korean firms that involve producing final products and providing post-production services for serving geographically separate foreign markets: high-income and low-income countries. I present a model in which heterogeneous firms must provide services for products through their subsidiaries in host countries, but can produce output in different locations. The model shows that the firm's equilibrium decision depends on its own productivity level and economic variables that affect production location and providing services. Using plant- and firm-level data of Korean firms, the empirical analysis provides the results that support the model's predictions. The second chapter analyzes the effects of regional economic integrations on investment patterns among Korean multinational firms. Using Korea's middle-income status, we develop a model in which heterogeneous firms in a middle-income country decide on the optimal FDI strategies for serving different regions: a developed (EEA) and a developing (AFTA) trade integrated regions. Following reduced trade costs between countries inside the trade integrated region, our model predicts that integrating into a regional economic zone affects firms with low productivity levels to enter the region via complex FDI strategies. Depending on the size of the region, however, complex FDI strategies differ such that firms investing in developed region tend to undertake local and export sales to the third country, whereas firms investing in developing region are more likely to engage in not only local and export sales to the third country, but also export sales to the parent country. The empirical analysis confirms the effect of different regional economic integrations on the strategy of firms with different productivity levels. The last chapter examines the conditions under which technology spillovers through workers' movement occur between foreign affiliates in the host country and determine whether such spillovers can affect the exporters' decisions to switch their strategies to serve foreign markets via FDI. Developing a simple two-period duopoly model, I find that the occurrence of technology spillovers is dependent on firm and host country characteristics such that spillovers are more likely to arise when firms have similar technology capabilities and in countries that incur low cost of training local workers. Under these circumstances, exporters are more likely to switch to FDI for serving foreign markets. However, I find that transport costs of goods have ambiguous effect on the occurrence of spillovers and thus, do not play a marginal role in exporters' decision. / text