This essay discusses the rhetoric of “authentic adaptation” in humanities adaptation studies, finding that, for the most part, authentic’s connotations of genuine or true have been interchangeable with faithful in fidelity discourses. Authentic is engaged far less frequently than its synonym largely, I argue, because authentic and adaptation are antonyms. The two terms furthermore forge a paradox in which adaptation’s definition has been adapted far less than authentic’s, which has been adapted to fit changing and competing epistemologies concerning what is true and genuine. I map authentic’s changing definitions onto adaptation discourses concerning fidelity to author intent, sources, oneself as adapter, consumer response, historical “truth,” material culture, and various phenomenological, philosophical, and psychological epistemologies to illuminate the relationship between authenticity and adaptation. Building on arguments made in Theorizing Adaptation, the chapter concludes that an authentic adaptation is one that is “true” to the processes and principles of adaptation: that is, to adaptation itself. Going beyond my prior work, I examine discourses of “authentic adaptation” in intercultural communications and their potential applications to humanities adaptation studies. The chapter concludes by considering discussions of authenticity in relation to that new form of adaptation, AI.