This Article introduces to legal scholarship the first sustained discussion of prison abolition and what I will call a “prison abolitionist ethic.” Prisons and punitive policing produce tremendous brutality, violence, racial stratification, ideological rigidity, despair, and waste. Meanwhile, incarceration and prison-backed policing neither redress nor repair the very sorts of harms they are supposed to address—interpersonal violence, addiction, mental illness, and sexual abuse, among others. Yet despite persistent and increasing recognition of the deep problems that attend U.S. incarceration and prison-backed policing, criminal law scholarship has largely failed to consider how the goals of criminal law—principally deterrence, incapacitation, rehabilitation, and retributive justice—might be pursued by means entirely apart from criminal law enforcement. Abandoning prison-backed punishment and punitive policing remains generally unfathomable. This Article argues that the general reluctance to engage seriously an abolitionist framework represents a failure of moral, legal, and political imagination. If abolition is understood to entail simply the immediate tearing down of all prison walls, then it is easy to dismiss abolition as unthinkable. But if abolition consists instead of an aspirational ethic and a framework of gradual decarceration, which entails a positive substitution of other regulatory forms for criminal regulation, then the inattention to abolition in criminal law scholarship and reformist discourse comes into focus as a more troubling absence. Although violent crime prevention and proportional punishment of wrongdoing purportedly justify imprisonment, this Article illuminates how the ends of criminal law might be accomplished in large measure through institutions aside from criminal law administration. More specifically, this Article explores a form of grounded preventive justice neglected in existing scholarly, legal, and policy accounts. Grounded preventive justice offers a positive substitutive account of abolition that aims to displace criminal law enforcement through meaningful justice reinvestment to strengthen the social arm of the state and improve human welfare. This positive substitutive abolitionist framework would operate by expanding social projects to prevent the need for carceral responses, decriminalizing less serious infractions, improving the design of spaces and products to reduce opportunities for offending, redeveloping and “greening” urban spaces, proliferating restorative forms of redress, and creating both safe harbors for individuals at risk of or fleeing violence and alternative livelihoods for persons subject to criminal law enforcement. By exploring prison abolition and grounded preventive justice in tandem, this Article offers a positive ethical, legal, and institutional framework for conceptualizing abolition, crime prevention, and grounded justice together.