Historians observe that printing diffused from Mainz in “concentric circles” (Barbier 2006). Distance from Mainz was significantly associated with early adoption of the printing press, but neither with city growth before the diffusion of printing nor with other observable determinants of subsequent growth. The geographic pattern of diffusion thus arguably allows us to identify exogenous variation in adoption. Exploiting distance from Mainz as an instrument for adoption, I find large and significant estimates of the relationship between the adoption of the printing press and city growth. I find a 60 percentage point growth advantage between 1500-1600.