Kant spent his long working life teaching at the university in the port of Königsberg, the Prussian town in which he was born. But even though he didn’t travel, he was an active participant in the philosophical debates of his time in Europe, and his ideas continue to shape and inﬂuence ﬁelds of philosophical inquiry from epistemology to the philosophy of history. From the perspective of the history of European thought in general, it is impossible to overestimate the importance of his later work, the critical philosophy published, in particular, in the texts, Critique of Pure Reason  and Critique of Practical Reason . From the point of view of international relations scholars, in addition to these works, Kant’s political writings, which also date from his ‘critical’ period, and in particular the essay On Perpetual Peace: A Philosophical Sketch , are also very signiﬁcant. Here I will highlight three areas of Kant’s critical thought that have helped set the scene for later critical theorists and for contemporary international relations scholarship: knowledge, morality, and politics.