Return innovation: The knowledge spillovers of the British migration to the United States, 1870-1940

This paper documents that out-migration promotes the diffusion of innovation from the country of destination to the country of origin of migrants. Between 1870 and 1940, nearly four million British immigrants settled in the United States. We construct a novel individual-level dataset linking British immigrants in the US to the UK census, and we digitize the universe of UK patents from 1853 to 1899. Using a triple-differences design, we show that migration ties contribute to technology diffusion from the destination to the origin country. The text analysis of patents reveals that emigration promotes technology transfer and fosters the production of high-impact innovation. Return migration is an important driver of this "return innovation" effect. However, the interactions between emigrants and their origin communities - families and neighbors - promote technology diffusion even in the absence of migrants' physical return.