Much of both the academic and practical discourse about international politics implies conceptions of states as, in one way or another, free or unfree. We talk about state autonomy, suggesting states have the capacity to deliberate and determine their own destiny. We discuss constraints on state action and debate the legitimacy of interference in the affairs of other states. We also measure and assess state development, suggesting a potential in states for self-realisation. The concept of sovereignty, and the belief that this principle demands the rejection of the subjection of states to higher authority, frames much of our thinking about world politics. Such issues lie at the heart of much of our theorising of IR: in realism's security dilemma, for example; in liberal debates about humanitarian intervention; or in constructivist analyses of the relationship between sovereignty and state identity. It is a central contention of this thesis that conceptions of state freedom are present in the deep analytical and normative presumptions of much of the theory of international relations. The conceptions of state freedom that inform such theorising remain, however, for the large part implicit. The principal purpose of this thesis is to remedy the absence of sustained, explicit consideration of the concept of state freedom, and it does this by historically excavating ideas about what it means for states to be free. While explicit discussion of the freedom of states was prominent in the 17th and 18th century, as the state's position as the locus of political authority was gradually consolidated the terminology of state freedom diminished in salience. Ideas of state freedom did not disappear, however; they continued to be expressed in analogous areas of international discourse. Drawing on philosophical ideas about individual freedom, this thesis presents a theoretical approach to making such implicit ideas visible. It makes the case for a 'grammar' of freedom, which, it is argued, enables one to distinguish ideas about freedom from other species of ideas but does not prejudice their substance. The thesis then employs this grammar to identify ideas of state freedom in international debate surrounding three cognate concepts: non-intervention, sovereign equality and self-determination. Through analysis of the arguments made by states-people about these three concepts, the thesis articulates a number of evolving ideas about what it means for states to be free and unfree. That historical investigation uncovers both a strong normative preference among practitioners of international relations for the freedom of states and sharp disagreement about what constitutes that freedom. The thesis argues that the contestation surrounding ideas of state freedom have played an important role structuring legitimate relations of control between states. The thesis concludes by reflecting on the implications of these observations for the approaches of theorists of international relations to the key concepts of sovereignty and the state.