This Element's focus is Kant's history of human reason: his teleological vision of the past development of our rational capacities from their very emergence until Kant's own 'age of Enlightenment.' One of the goals is to connect Kant's speculative account of the very beginning of rationality – a topic that has thus far been largely neglected in Kantian scholarship – to his well-known theory of humankind's progress. The Element elucidates Kant's hopes with regard to reason's future progress and his guidelines for how to achieve this progress by unifying them with his vision of reason's past. Another goal is to bring more attention to Kant's essay 'Conjectural Beginning of Human History,' where this account is presented, and to show that this unusual text does not stand in conflict with Kant's philosophy and is not merely tangentially related to it, but illuminates and complements certain aspects of his critical philosophy.