Because it laid the foundation for nearly all subsequent epistemologies, Immanuel Kant’s Critique of Pure Reason has overshadowed his other interests in natural history and the life sciences, which scholars have long considered as separate from his rigorous theoretical philosophy—until now. In Kant’s Organicism, Jennifer Mensch draws a crucial link between these spheres by showing how the concept of epigenesis—a radical theory of biological formation—lies at the heart of Kant’s conception of reason. As Mensch argues, epigenesis was not simply a metaphor for Kant but centrally guided his critical philosophy, especially the relationship between reason and the categories of the understanding. Offsetting a study of Kant’s highly technical theory of cognition with a mixture of intellectual history and biography, she situates the epigenesis of reason within broader investigations into theories of generation, genealogy, and classification, and against later writers and thinkers such as Goethe and Darwin. Distilling vast amounts of research on the scientific literature of the time into a concise and readable book, Mensch offers one of the most refreshing looks not only at Kant’s famous first Critique but at the history of philosophy and the life sciences as well.