The philosophical kinship between Kant and the Stoics is often noted in passing but has received relatively little sustained scholarly attention. This detailed, wide-ranging study shows Kant's engagement with Stoic philosophy to extend beyond ethics, tracing its impact on Kant's inquiry on rationality, moral psychology, human action, and the concept of nature as well. It reveals that Kant's most philosophically productive engagement with Stoic thought comes not in the more familiar ethical works of the critical decade (the Groundwork and the second Critique), but rather in his later practical works examining human development, moral progress and virtue, and cosmopolitan duty. This book distinctively highlights the pivotal role that the 1790 Critique of the Power of Judgment plays in Kant's appropriation and transformation of Stoic ideas, as well as his close dialogue with Seneca and Epictetus throughout the 1793 Religion within the Bounds of Reason Alone.