This article presents evidence that cultural proximity between the exporting and the receiving countries positively affects the adoption of new institutions and the resulting long-term economic outcomes. We obtain this result by combining new information on pre-Napoleonic principalities with county-level census data from nineteenth-century Prussia. We exploit a quasi-natural experiment generated by radical Napoleonic institutional reforms and the deeply rooted cultural heterogeneity across Prussian counties. We show that institutional reforms in counties that are culturally more similar to France, in terms of religious affiliation, generate better long-term economic performance.