Abstract: The central contention of this article is that contemporary liberal theory is without an account of what legitimates coercing those who reject liberalism that is consistent with its own stipulations of the conditions of political legitimacy. After exploring the nature of the liberal principle of legitimacy, and in particular how it is intended to function as a way of protecting individuals from domination and oppression by reconciling freedom and public law, the article considers four different possible accounts of what might legitimate coercing non-liberals. While some of them have independent plausibility, the article argues that none of them meets the requirements of liberal legitimacy. The final section of the article considers the implications of this theoretical gap for liberal theory more widely. The argument is made that liberalism must accept that even liberal politics will necessitate the oppressive use of coercive power, i.e. compelling people to live according to wills other than their own, and that insofar as this is a position central to the recent burgeoning literature on political realism, liberalism ought therefore to be more realist.