With the increasing scale and complexity of immigration, an important question is: what are the economic consequences of this massive mobility? This thesis focuses on consequences of international migration and the associated growing cultural diversity. The empirical findings of the thesis from national, regional and firm level analyses demonstrate that the demographic, human capital and cultural composition of immigration is more important than the size of the immigrant population for innovation and economic growth. Furthermore, immigrants can be beneficial both at the firm and the regional levels to facilitate international, interregional and within firms’ knowledge spillovers and increasing productivity. The thesis shows that with their talent and unique combination of diverse backgrounds, immigrants increase the ability of firms to innovate products and services.