The causes of the Protestant Reformation have long been debated. This paper seeks to revive and econometrically test the theory that the spread of the Reformation is linked to the spread of the printing press. I test this theory by analyzing data on the spread of the press and the Reformation at the city level. An econometric analysis that instruments for omitted variable bias with a city's distance from Mainz, the birthplace of printing, suggests that cities with at least one printing press by 1500 were at minimum 29 percentage points more likely to be Protestant by 1600.