This paper examines the impact of immigrant innovators on the global activities of U.S. firms by analyzing detailed data on patent applications and the operations of the foreign affiliates of U.S. multinational firms. The findings show that when a greater share of a firm’s innovation is carried out by inventors of a particular ethnicity, the firm’s affiliate activity in those inventors’ native countries increases. Additionally, ethnic innovators help facilitate the spread of innovative activities across borders and enable U.S. multinationals to establish new affiliates abroad without needing local joint venture partners. Thus, the study highlights how immigration can boost the competitiveness of multinational firms.