This article examines Nietzsche’s engagements with Kantian idealism and Kantian ethics. From the mid-1860s to the mid-1870s, Nietzsche’s engagement with Kantian idealism combined an interest in its potential therapeutic and cultural benefits with an exploration of its theoretical difficulties. In later works, Nietzsche rejects Kantian idealism not only for the conceptual incoherence, epistemological insignificance, and suspicious psycho-physical and cultural functions of its notion of an inaccessible reality, but also for the unlicensed ontology and primitive psychology of its notions of judgement. Nietzsche also developed his own version of ‘Kantian’ ethics—that is, an ethics which, like Kant’s, affirms agency as the highest and unconditional value, while, unlike Kant’s, admitting different degrees of agency and therefore moral significance, across agents and over time.