In this paper, we study the effects of economic integration with democratic partners on democracy. We assemble a large country-level panel dataset from 1960 to 2015, and exploit improvements in air, relative to sea, transportation to derive a time-varying instrument for economic integration. We find that economic integration with democracies increases countries’ democracy scores, whereas the impact of economic integration with non-democracies is muted. Results are stronger when democratic partners have a longer history of democracy, grow faster, spend more on public goods, are culturally closer, and export higher quality goods. The effects we document are driven by imports, rather than exports, and by integration with democratic partners that account for a larger share of a country’s trade in institutionally intensive, cultural, and consumer goods, as well as in goods that involve more face-to-face interactions and entail higher levels of bilateral trust. These patterns are consistent with economic integration favoring the transmission of democracy by signaling the (actual or perceived) desirability of democratic institutions. Alternative mechanisms—including human capital accumulation and economic growth—cannot, alone, explain our findings.