This thesis draws on the principle of moral equality to develop a novel critique of a range of practices apparently licensed by the idea that the state has a right to exclude. The state’s right to exclude can be understood as consisting of three conceptually distinct rights: a right to exclude outsiders from its territory, a right to exclude them from settling within the territory, and a right to exclude them from acquiring citizenship status. It is widely acknowledged that the right to exclude has its limits. But on what grounds do we think the right to exclude must be limited, and how extensive are those limits? It is common to argue that the right to exclude must be constrained by the principle of moral equality: the idea that all persons are of equal moral worth, by virtue of their shared humanity. Indeed, in the existing literature, there has been one powerful attempt to show that the right to exclude always violates the requirements of moral equality, by distinguishing between citizens and non-citizens on the basis of a factor that is morally arbitrary: their nationality. According to that line of argument, there can be no right to exclude. In this thesis, I make a different move. I argue that we need to pay attention to the ways in which exercises of the right to exclude violate another key demand that emerges from the idea that we are all of equal moral worth. I focus on the idea of social equality, and on the relationship between this and the demand for respect. The central claim of my thesis is that borders do not just passively stand in the way, blocking people from pursuing the equal opportunities to which they are entitled. The exercise of the right to exclude also actively licenses disrespectful policies towards non-citizens, and in some cases, citizens as well. I examine three such examples: the detention and deportation of non-citizens, discrimination against low-skilled migrants, and the denationalization of citizens who are dual nationals, for the purposes of national security. In order to uphold the demands of moral equality, we need to rethink the existing social structures and institutional contexts that are bound up with states’ exercise of the right to exclude.