Governor partisanship explains the adoption of statewide mandates to wear face coverings. Christopher Adolph, Kenya Amano, Bree Bang-Jensen,Nancy Fullman, Beatrice Magistro, Grace Reinke, and John Wilkerson: “Public mask use has emerged as a key tool in response to COVID-19. We develop and document a classification of statewide mask mandates that reveals variation in their scope and timing. Some U.S. states quickly mandated the wearing of face coverings in most public spaces, whereas others issued narrow mandates or no mandate at all. We consider how differences in COVID-19 epidemiological indicators, state capacity, and partisan politics affect when states adopted broad mask mandates. The most important predictor is whether a state is led by a Republican governor. These states were much slower to adopt mandates, if they did so at all. COVID-19 indicators such as confirmed cases or deaths per million are much less important predictors of statewide mask mandates. This finding highlights a key challenge to public efforts to increase mask-wearing, widely believed to be one of the most effective tools for preventing the spread of SARS-CoV-2 while restoring economic activity.”