The margin of appreciation is a judicial doctrine whereby international courts allow states to have a measure of diversity in their interpretation of human rights treaty obligations. The doctrine is at the heart of some of the most important international human rights decisions. Does it undermine the universality of human rights? How should judges decide whether to give this margin of appreciation to states? How can lawyers make best use of arguments for or against the margin of appreciation? This book answers these questions, and broadens the discussion on the margin of appreciation by including material beyond the ECHR system. It provides a comprehensive justification of the doctrine, and catalogues the key cases affecting the doctrine in practice.