A distinct feature of the Protestant Reformation was Martin Luther's intentional use of the vernacular (German), rather than Latin, in his writings in order to engage the laity in theological discussions. This paper studies the impact of the Protestant Reformation on the use of the vernacular in the Holy Roman Empire. We show that immediately after 1517, there was a sharp rise in religious vernacular printing output, especially in Protestant but also in Catholic printing cities. Moreover, and importantly, we find similar patterns for printed texts outside the religious realm. In turn, within decades after the Reformation vernacular works became widely available throughout the Holy Roman Empire. Exploiting variation within Catholic and within Protestant printing cities, we provide evidence on the underlying mechanism. We document that the Reformation, by increasing religious competition, reduced the Catholic Church's influence on language use in printing, and that it contributed to the standardization of the German language. We then turn to language change in education and show that the Reformation led to a significant increase in the number of German schools in Protestant printing cities relative to Catholic ones. All in all, our results suggest that the Reformation played a decisive role in promoting the use of the vernacular in two important domains--printing and education--in the Holy Roman Empire.