Why do some criminal justice public policies spread rapidly throughout U.S. states, and other policies never take hold? To answer this question, this article presents the first review specifically of studies that have examined the diffusion of criminal justice policies throughout U.S. states. After a comprehensive review of key research databases, 23 studies are identified. The key findings of these studies are analyzed in great depth, with particular reference to cross-study differences in how three variables from the general policy literature—geographic proximity, political ideology, and media attention—were operationalized. The article identifies important gaps in current knowledge about the factors that affect the diffusion of criminal justice policies and suggests several directions for future research in this area.