Although many of the pioneers of behavior analysis thought on a large scale and encouraged others to do so, most behavior analytic projects have remained small scale. The intent of this article is to urge the application of behavior analytic principles on a large scale. This article begins with a brief history of applied behavior analysis. It then describes some early behavior analysts who thought big and describes several examples of large-scale behavioral projects. It then shows how behavior analysis fits well with the public health model and describes how behavior analytic principles can be implemented broadly to combat public health problems. The article ends with some practical advice for behavior analysts on how to think big and speculates on the future of behavior analysis.