Standard neoclassical models of economic integration are based on the assumptions that capital and labor are substitutes and that the geography of factor market integration does not matter. Yet, these two assumptions are violated if agglomeration forces among factors from specific source countries are at work. Agglomeration implies that factors behave as complements and that the country of origin matters. This paper analyzes agglomeration between capital and labor empirically. We use state-level German data to answer the question whether and how migration and foreign direct investment (FDI) are linked. Stocks of inward FDI and of immigrants have similar determinants, and the geography of factor market integration matters. There are higher stocks of inward FDI in German states hosting a large foreign population from the same country of origin. This agglomeration effect is confined to higher-income source countries.