Many innovation studies focus on adoption behaviors at the individual and organizational level, while studies examine innovation adoption at the community and population level is relatively limited. These studies, focusing on the diffusion of an innovation across organizations, are important as they illustrate the dynamics of adoption behaviors in a broader context of socio-political factors. In this review study, we examine three prominent diffusion theories: classic diffusion theory, institutional diffusion theory, and cognitive-institutional diffusion theory. We identify the underlying diffusion mechanism in each theory. Future research is needed to show how these diffusion mechanisms interact in creating various diffusion patterns.