The debate over rival conceptions of political legitimacy tends to focus on first-order considerations—for example, on the relative importance of procedural and substantive values. In this essay, I argue that there is an important, but often overlooked, distinction among rival conceptions of political legitimacy that originates at the meta-normative level. This distinction, which cuts across the distinctions drawn at the first-order level, concerns the source of the normativity of political legitimacy, or, as I refer to it here, the grounds of political legitimacy. If we focus on the grounds of political legitimacy, there are three main conceptions of political legitimacy: will-based, belief-based, and fact-based conceptions. I present an objection to each of those main conceptions and defend a hybrid account of the grounds of political legitimacy.