The three essays of this dissertation focus on estimating the heterogeneity in immigrants\u27 performance in the host country\u27s economy across skill levels. This dissertation research provides new estimates and perspectives on immigrants\u27 impact on host countries\u27 economies using cross-country and country-specific data. The first essay examines the causal linkage between ethnic networks and bilateral trade across different skill groups of immigrants and products\u27 quality levels. The results suggest that a higher level of human capital provides high-skilled migrants with opportunities to trigger more high-quality trade than the low-skilled migrants. Low-skilled migrants also use their home country knowledge to their advantage to...