This study represents the most comprehensive attempt yet to assess what motivates scientists to engage with the public in the United States. Through a set of parallel surveys of scientists from multiple scientific societies (N = 9,244) we found that the most consistent predictors of a scientist’s willingness to take part in engagement activities with the public are a belief that she or he will enjoy the experience (attitude), make a difference through engagement (response efficacy), and has the time to engage. Age, sex, what a scientist thinks about the public, perceived personal engagement skill (self-efficacy), and what a scientist thinks about her or his colleagues (normative beliefs) were inconsistent predictors. Furthermore, these predictors of willingness seem to work relatively well when looking at any of the three engagement modes—face-to-face, online, and through media—and across any of the types of scientists studied here. Together, the results might be understood as providing the most comprehensive look to date on the factors that are associated with scientists’ willingness to engage.