This article examines the philosophical sources for Kant's interpretation of Plato's Republic and its impact on his conception of the ideal state. I argue that Kant's knowledge of Plato was not derived from Plato's writings, but from secondary accounts. More specifically, I focus on four authors whose discussions of Plato influenced Kant's understanding of the perfect republic: Brucker, Cicero, Wolff, and Rousseau. Two main claims emerge. First, I show that Kant's appeal to the Republic intervenes in a longstanding debate about (...) the irrational and “enthusiastic” character of Platonic idealism. Second, I emphasize Rousseau's role in instigating Kant's interest in Plato and shaping his conception of the perfect, fully self‐legislating republic that serves as the regulative norm of the state which existing regimes can and should strive to emulate. The result of my analysis is a better understanding of Kant's relationship to Plato and Rousseau, as well as the philosophical motivations behind his version of the ideal republic. (shrink)