Of late, risks of human extinction (or so-called 'existential risks') have become the target of an emerging field of scientifically serious study. We are now increasingly conversant with increasingly distal and severe futurities. Such a dynamic, of incremental entanglement with futurity, typifies the growing edge of modernity. Yet this dynamic is not itself without a history. Or, we have been being swept up in the future for quite some time now. This thesis attempts to supply the history of the incipience of this dynamic, by interrogating the Enlightenment bases and beginnings of our grasp of human extinction and existential risk. In so doing, it hopes to begin to supply a richly recollective dimension to the field of 'future studies'. Indeed, the story of how we came to be aware of our extinction invokes not only the history of rationality but also the rationality of history, inasmuch as recollecting the idea's Enlightenment provenance unveils study of X-risk to be a question of 'enlightening' in an integral and indissociable sense, which thereby contextualizes today's investigations on the topic as a vital continuation of the as-yet-unfinished project of Enlightenment and its tenacious task for the human race. Accordingly, the thesis argues for the uniquely scientific and modern provenance of the idea of human extinction, as opposed to the perennial tradition of religious eschatology. In short, where apocalypse secures a sense of an ending, extinction anticipates the ending of sense. As different in kind, not degree, they are utterly different in origins. Prospective grasp of our extinction first emerges, in the eighteenth-century, due to the maturation of three key scientific vocabularies. These included the emergence of the geosciences, the consolidation of demography and political arithmetic, and the development of a rigorous and mathematized notion of risk and uncertainty. Suitably, some of the first prognoses upon our extinction emerge from such fields. Yet, these empirical vocabularies were necessary but not sufficient for the foment of future forecast concerning extinction threats. Grasp of existential risk didn't merely require breakthroughs in description of fact alone: it additionally demanded in-step reflections upon the propriety and position of value and reason as such. In other words, we had to first realize the cosmos isn't imbued with inherent justice and value, which required self-reflection upon the nature of normativity as much as ground-level empirical inquiries. Acknowledgment that our values would not be persistent and ongoing features of the natural world independently of our stewardship and guardianship of them was requisite before we could be at all motivated to preemptively protect them against an extra-judicial nature. In short, we had to discover that sapient value is cosmically precarious before we could appreciate that it was cosmically precious, and, through this, be summoned to the modernity-defining tasks of prediction, mitigation, and strategizing. This. then, was the incipience of our hyper-modern tendency to become incrementally entangled in the future. Insofar as extinction therefore required philosophical reflection as much as empirical investigation, Immanuel Kant emerges as a key figure throughout. It was Kant, after all, who influentially defined Enlightenment itself as humanity's progressive undertaking of responsibility for itself: and it is the conviction of this thesis that today's increasing awareness and sensitivity to existential risk is just part and parcel of this still-ongoing task and trajectory. For, one is only responsible for oneself to the extent that one is receptive to the perils one faces, and, thereby, is in the first place motivated to become responsive to such hazards. And, in this sense, it ultimately becomes possible to contextualize today's emerging field of existential risk studies as consolidating from out of this progressive historical sweep, stretching all the way back to the Enlightenment and Kant's question 'What is Enlightenment?'. The conclusion, then, is that, in order to care about X-risks, we first had to separate 'fact' from 'value' so as to understand the stakes involved in the prospective 'fact' of the end of all 'value'. Only through this were we summoned to the tenacious tasks of forecast and foresight. And, ultimately, it is solely by undertaking such responsibility for ourselves, via acknowledging the utmost risk facing us, that we begin to earn security and hope.