Immanuel Kant’s claim that the categorical imperative of morality is based in practical reason has long been a source of puzzlement and doubt, even for sympathetic interpreters. In The Form of Practical Knowledge, Stephen Engstrom provides an illuminating new interpretation of the categorical imperative, arguing that we have exaggerated and misconceived Kant’s break with tradition. By developing an account of practical knowledge that situates Kant’s ethics within his broader epistemology, Engstrom’s work deepens and reshapes our understanding of Kantian ethics.