Both international and domestic laws have long forbidden the abuse and torture of prisoners. Specifically, international law forbids 'cruel, inhuman and degrading treatment,' a form of illegal abuse that has no codified definition in international law. In this dissertation chapter, I argue that many courts and scholars have failed to adequately conceptualize this prohibition, mistakenly lumping inhuman and degrading treatment under the category of cruelty. I conclude that because of this blurring of the distinction between cruel, inhuman and degrading treatment, the scope of the treatment that is understood to be legally prohibited has been unnecessarily narrowed, permitting many forms of institutional abuse to remain unrecognized by courts. I also conclude that this narrow approach overlooks many forms of institutional treatment that should be prohibited, in part for legal consistency, and in part to safeguard the wellbeing of prisoners. Drawing on 78 interviews with former Guantanamo detainees, I demonstrate that “the worst” prison treatment, for many prisoners, is not physical cruelty as often assumed, but treatment that can be categorized as inhuman and/or degrading, and thus that these phenomena are necessarily distinct. Based on this finding, I make the normative argument that society’s understanding of the prohibition against cruel, inhuman and degrading treatment must be refined and reconsidered, if some of the worst prison-based atrocities are to be avoided.