Public health officials recommend wearing a mask to reduce the spread of COVID-19, yet individual compliance varies. Understanding the full range of determinants of mask-wearing is critical for promoting evidence-based public health solutions to slow the spread of COVID-19. Using data from a survey of 3,059 respondents across six US states, this study investigates the relationship between psychological factors, including threat- and efficacy-related perceptions, on mask-wearing behavior. It is found that respondents’ perceptions of self-efficacy (e.g., ability to wear a mask) and response efficacy (e.g., effectiveness of mask-wearing in reducing COVID-19 transmission) better predict mask-wearing behavior than a number of commonly cited sociodemographic factors. These results suggest that messaging focused on the relative ease and effectiveness of mask wearing may help increase compliance with public health recommendations for mitigating COVID-19. Read more.