Kant is well known for claiming that we can never really know our true moral disposition. He is less well known for claiming that the injunction “Know Yourself” is the basis of all self-regarding duties. Taken together, these two claims seem contradictory. My aim in this paper is to show how they can be reconciled. I first address the question of whether the duty of self-knowledge is logically coherent (§1). I then examine some of the practical problems surrounding the duty, notably, self-deception (§2). Finding none of Kant’s solutions to the problem of self-deception satisfactory, I conclude by defending a Kantian account of self-knowledge based on his theory of conscience (§3).