The fundamental question of political philosophy is whether there should be a state at all. This question arises because states are coercive. States utilise force as well as the threat of force to make those who are within their territory comply with the laws that they have promulgated. Explaining how they can permissibly do so is necessary for justifying the state. First, one needs to show how and under what conditions the state is justified in using coercion. Second, one has to justify the monopoly on coercion, explaining on what grounds the state occupies a privileged position so that it can forbid others from likewise using coercion. And, third, one needs to provide an explanation of the territorial dimension of the state, justifying how the state comes to occupy this privileged position with respect to a particular territory. Each of these tasks is fraught with difficulties. The coercion on the part of the state runs up against the liberty and autonomy of individuals. The monopoly on coercion requires one to introduce an asymmetry amongst moral equals, granting powers and permissions to some that others do not have. And, finally, the territorial nature of the state requires one to draw boundaries that exclude those who are outside them. These difficulties put substantial pressure on the idea that states can ever be justified. The project Authority and Territory aims to address these challenges by systematically developing a novel Kantian justification of the state. It argues that the state is not optional but morally necessary and, correspondingly, that the state need not be based on consent but can permissibly be established and maintained by coercion. By developing a distinctively normative assurance problem, it offers a reconceptualisation of the fundamental problem that makes the state necessary in the first place. In particular, it shows why the state of nature is, from a normative perspective, a condition of war and correspondingly why the state is necessary in order to establish a condition of peace in which interactions are rightful. As a result of reconceptualising the Kantian approach to political obligation in terms of a natural duty of peace, rather than in terms of the traditional natural duty of justice, it manages to particularise political obligation on the part of individuals and to establish the territorial aspect of the state, thereby showing how authority on the part of the state can be particularised and how the boundary problem can be solved within a functional account.