Immanuel Kant's essay on Perpetual Peace (1795/96) contains a rejection of the idea of a world government (earlier advocated by Kant himself). In connexion with a substantial argument for cosmopolitan rights based on the human body and its need for a space on the surface of the Earth, Kant presents the most rigorous philosophical formulation ever given of the limitations of the cosmopolitan law. In this contribution, Kant's essay is analysed and the reasons he gives for these restrictions discussed in relation to his main focus: to project a realistic path to perpetual peace.