This study evaluates the impact of high-skilled immigrants on US technology formation. Specifically, we use reduced-form specifications that exploit large changes in the H-1B visa program. Fluctuations in H-1B admissions levels significantly influence the rate of Indian and Chinese patenting in cities and firms dependent upon the program relative to their peers. Most specifications find weak crowding-in effects or no effect at all for native patenting. Total invention increases with higher admission levels primarily through the direct contributions of ethnic inventors.