Kant takes the idea of autonomy of the will to be his distinctive contribution to moral philosophy. However, this idea is more nuanced and complicated than one might think. In this chapter, I sketch the rough outlines of Kant’s idea of autonomy of the will while also highlighting contentious exegetical issues that give rise to various possible interpretations. I tentatively defend four basic claims. First, autonomy primarily features in Kant’s account of moral agency, as the condition of the possibility of moral obligation. Second, autonomy amounts to a metaphysical property as well as a normative principle and a psychological capacity. Third, although there is legitimate scholarly disagreement about whether or not autonomy involves self-legislation of the moral law, there is good reason to believe it underwrites an ‘inside-out’ (as opposed to ‘outside-in’) conception of the relationship between the will and moral requirements. Fourth, persons have dignity because their autonomy makes them members in the set of beings over whom the categorical imperative requires us to universalise our maxims, not because autonomy is an independently important property.