This paper examines how proposed U.S. restrictions on international students would affect the nation’s STEM workforce and long-run economic growth. Focusing on the most common pipeline from U.S. universities to the labor market, we show that international education is the principal mechanism by which the United States recruits and retains high-skill STEM talent. We present survey evidence suggesting that proposed policy changes will deter substantial numbers of international students from studying in the United States and remaining in its workforce after graduation. We then estimate the effects of plausible policy-induced declines in the number of foreign STEM graduates entering the U.S. workforce. A sustained one-third reduction would shrink the high-skill STEM workforce by about 6 percent overall, potentially by more than 11 percent at the Ph.D. level, and would lead to long-run GDP losses of $240 billion to $481 billion annually. These losses are unlikely to be offset by U.S.-born workers or foreign-trained workers abroad. Drawing on evidence on innovation, entrepreneurship, and spillovers, we conclude that restricting this talent pipeline would weaken innovative capacity and long-run productivity in the U.S. economy.