This book tracks the political history and specific political actions associated with the diffusion of state-level marijuana decriminalization. It provides an integrated chronology of policy diffusion to show how social and cultural changes have impacted the shift from anti- to pro-marijuana political platforms. The main contributions are an interdisciplinary approach to analyzing policy learning and evolution, an overview of the political history of marijuana criminalization, a clear synthesis of the medical literature on cannabis effects, and a supply and demand analysis of legal and illegal marijuana markets in America. For scholars of criminal justice, law, political science, policy studies, sociology and addiction, it provides an amalgam of the diverse and divergent extant research on marijuana.