While almost all of Kant’s contemporaries agreed that the Critique of Pure Reason effected a philosophically epochal change, there was far less consensus about what precisely Kant’s new critical philosophy had brought about. In large part, this uncertainty was a result of a methodological crisis that Kant’s work had sparked: the Critique had shown that traditional dogmatic metaphysics was suspect at best, but what new methods needed to be adopted in the wake of Kant’s ‘Copernican Revolution’? The Critique stood as the lighting rod at the center of a complicated and especially lively set of debates and disputes that erupted in Germany in the late 1780s and early 1790s: empiricists and rationalists, threatened by the ‘all-destroying Kant’, leapt to challenge the new critical system; skeptics attacked Kant’s claims to have secured a sure footing for empirical knowledge; a few ambitious thinkers sought to complete the critical system by revealing a foundational first principle on which Kant’s system could rest. All of these elements conspired to make the early stages in post-Kantian thought one of the richest, most vibrant – and most fascinating – periods in the history of philosophy. The present essay looks at the various figures of the move from Kant to Fichte, and presents some of the excellent new research on the era that has appeared in the last decade or so. The sequel takes up the period from Fichte to Hegel, with an eye toward understanding how Kantian critical philosophy gave way to Hegelian Absolute Idealism.