Migration of ideas comes not only from permanent migrants but also from temporary migrants, such as international students, conference attendees, and visitors at foreign laboratories and centers. Given that collaborations generally arise from personal connections (1), it is hard to imagine internationally coauthored research expanding absent researcher mobility. Ties between U.S. and Chinese researchers exemplify how migration advances knowledge and benefits source and destination country. The United States is the top destination of Chinese international students and postdocs, and China is the top source of foreign students in the United States, and they contribute to U.S. scientific productivity (2). Those who return to China tend to outperform other Chinese researchers in terms of citations in international scientific journals (3). Homophily in citations suggests that a paper with authors from two countries is likely to spread new ideas or findings more rapidly across borders than if the paper's authors were from the same country. Having a foreign collaborator with a network of researchers in another country usually attracts overseas attention to research. In scientific work, China and the United States are each others' biggest partners: 16% of U.S. international collaborations are with China, and 48% of China's international collaborations are with the United States (4). U.S. corporations conduct research and patent inventions in China, and Chinese firms buy U.S. start-ups and patent in the United States. About 15% of author names on papers written at U.S.-based institutions are Chinese, whose first names (e.g., Xu rather than David) identify them as born overseas (5). Connections between migrants and natives on papers, patents, and citations does not directly measure the migration of ideas, which requires latent semantic analysis of the content of the underlying documents. But network links between collaborators from different countries establish a prima facie case for policies that treat foreign-born students and migrant researchers as valuable contributors to the United States and home-country scientific and economic progress and as possible future U.S. citizens as well.