In this thesis I argue that nations can have a right to unilaterally secede from a legitimate, non-usurping state. In addition, I argue that they are special in this regard. I argue that there is a presumption in favour of collective autonomy by nations, establishing this claim by showing that co-nationality can be an intrinsically valuable relationship and that this grounds a strong claim to self-determination. I then argue that there are no considerations that always defeat the presumption in favour of collective autonomy by nations-for example, unilateral secession from a legitimate state need not wrong citizens of the remainder state by wrongfully taking territory. As such, nations can have an undefeated claim right to unilaterally secede from a legitimate state. I establish the second part of the claim above-that nations are special in this regard-in two ways. First, I argue against more permissive accounts of self-determination; accounts that attempt to ground a right to secede for any territorially concentrated group capable of performing the basic functions of statehood and governing in a satisfactory manner. Secondly, I argue that despite the fact that other kinds of group-such as religious groups-share the features in virtue of which nations have a claim to self-determination, the content of these groups' identities is too narrow to be the basis of a pluralistic political identity, and such, they would wrong members of minority groups within their territory by seceding. This is not true of nations, I argue.