When scientists and engineers immigrate to the United States, is it an important and enabling enhancement for our high-tech economy, or does it discourage and displace natives who would otherwise fill the jobs that these foreigners take? There is no shortage of entrenched views and vehement arguments on all sides of such questions. Though very little reputable research had been done on this subject not so many years ago, now immigration policy for highly skilled workers has become a controversial and polarizing topic among both politicians and academics. What is needed are dispassionate empirical studies of how the immigration of highly skilled workers can affect wages, employment, innovation, and productivity. This grant will support the work of Sari and William Kerr, rare examples of immigration researchers who are themselves highly skilled, but who are not readily associated with any political, methodological, or ideological camps. Rather, they have a reputation for working with interesting data, then letting the results fall where they may and speak for themselves. Their research under this grant will make pioneering use of sophisticated datasets that have only recently become available, including the Longitudinal Employer-Household Dynamics (LEHD) files now maintained by the U.S. Census Bureau. Their work will be the first study of highly skilled immigration based on data and analysis at the firm level. The project will also address the question of whether firms are substituting younger highly skilled immigrants for older highly skilled native workers.