The Final Frontier examines the language employed in Zoroastrian and Manichaean textual, ritual, and iconographic traditions to articulate eschatological notions. Bringing together twelve original contributions by leading scholars, the volume investigates how Iranian religious sources conceptualize death, the afterlife, and communication with the transcendent world, while also engaging in comparative dialogue with Christian traditions. A central focus of the volume is metaphorical language. By combining Conceptual Metaphor Theory with close philological analysis of Avestan and Middle Persian sources, the studies investigate how metaphors structured around notions such as journey, chariot race, kingship, light, darkness, fragrance, royal architecture, and spatial ascent function as primary cognitive frameworks through which the ineffable is rendered conceptually accessible. The integration of cognitive approaches, historical linguistics and the study of Iranian religions offers a new perspective on the analysis of the language of eschatology and the conceptual foundations of religious thought.