This paper assesses the extent to which the international migration of inventors affects innovation in the receiving country. Drawing on a novel database that maps the migratory patterns of inventors, we exploit the end of the Soviet Union and the consequent post-1992 influx of ex-Soviet inventors to the United States. Econometric analysis on a panel of U.S. cities and technological fields shows that the patenting activity of U.S. inventors increased significantly after the arrival of ex-Soviet Union inventors.