This book provides an accessible introduction to Kantian constitutional theory and the law and politics of European rights protection. Part I sets out Kant's blueprint for achieving Perpetual Peace, and to the elaboration of a Kantian-congruent model of constitutional justice, both within and beyond the nation state. Part II applies this theoretical framework to explain the gradual constitutionalization of a cosmopolitan legal order: a transnational legal system in which justiciable rights are held by individuals; where public officials bear the obligation to fulfil the fundamental rights of all who come within the scope of their jurisdiction; and where domestic and transnational judges supervise how officials act. The book argues that this order has emerged in Europe thanks to the combined effects of Protocol no. 11 (1998) of the European Convention on Human Rights and the incorporation of the Convention into national law. The book covers the strengthening of the Court's capacities to meet the challenge of chronic failures of protection at the domestic level; its progressive approach to "qualified" rights, including privacy and family life, freedoms of speech, assembly, the press, conscience, and religion; the robust enforcement of "absolute" rights, including the prohibition of torture and inhuman treatment; and the Court's aim to render justice to all people that come under its jurisdiction, even non-citizens who live - and whose rights are violated - beyond Europe. It explains how the European Court of Human Rights has become one of the most active and important advocates for human rights in the world, while helping to construct a nascent cosmopolitan constitution in Europe.