We examine business creation by Ukrainian refugees in Poland following the Russian invasion of Ukraine. Using registry data, we show that Ukrainians started 38,833 firms in 2022?23, accounting for 7% of all new registrations in Poland. We link this entrepreneurship to refugees in two ways. First, our survey shows that 58% of post-invasion Ukrainian founders registered as refugees. Second, cross-county regressions show that a 10% increase in adult male Ukrainian refugees is associated with a 2.71% increase in Ukrainian firm registrations. We then show that new Ukrainian businesses stimulate rather than crowd out Polish entrepreneurship. Using a shift-share strategy based on refugee shocks and Ukrainians’ comparative advantage, we find that a 10% increase in Ukrainian registrations led to 2.31% more Polish firms. Survey evidence suggests two mechanisms: emulation, with 59% of Ukrainian owners reporting Polish entrepreneurs starting similar firms, and supply-chain linkages, with 88% of Ukrainian firms engaged in local business-to-business transactions.