In less than a decade, marijuana legalization has gone from unthinkable to seemingly unstoppable. This essay — written for a special issue on improving Arizona’s criminal justice system — discusses how Arizona should best advance marijuana legalization so that it can significantly improve Arizona’s criminal justice system. Now that Arizona has legalized marijuana via ballot initiative, we do not wade too deeply into the arguments for and against legalization or the criminal justice impact inherent in the repeal of prohibition (such as reductions in marijuana arrests and sentences). Instead, we focus on steps that Arizona policymakers and advocates who are interested in improving the criminal justice system can take to ensure that legalization best advances this goal. First, we set the stage in Part I with a brief history of marijuana prohibition, its role in criminal enforcement today, and the movement to enact state legalization laws. In Part II, we turn our attention to Arizona, beginning with a description of marijuana reform efforts in Arizona and key facets of the Smart and Safe Arizona Act. We then provide recommendations for policymakers and other concerned parties about how to ensure modern marijuana reforms in Arizona (and elsewhere) can and should help build a reform infrastructure that could not only ensure record relief to redress past marijuana convictions but also address broader criminal justice issues that historically intersect with marijuana prohibition.