This book explores secession from three normative disciplines: political philosophy, international law and constitutional law. The author first develops a moral theory of secession based on a hypothetical multinational contract. Under this contract theory, injustices do not determine the existence of a right to secede, but the requirements to exercise it. The book second part then argues that international law is more inclined to accept and advance a remedial right approach to secession. Therefore, justice as multinational fairness is to be fully institutionalized under the constitutional law of liberal democracies. The final part proposes constitutionalizing a qualified right to secede with the aim of fostering recognition and accommodation of national pluralism as well as cooperation and compromise between majority and minority nations.