One of the most noted developments in international law over the past twenty years is the proliferation of international courts and tribunals. They decide who has the right to exploit natural resources, define the scope of human rights, delimit international boundaries and determine when the use of force is prohibited. As the number and influence of international courts grow, so too do challenges to their legitimacy. This volume provides new interdisciplinary insights into international courts' legitimacy: what drives and undermines the legitimacy of these bodies? How do drivers change depending on the court concerned? What is the link between legitimacy, democracy, effectiveness and justice? Top international experts analyse legitimacy for specific international courts, as well as the links between legitimacy and cross-cutting themes. Failure to understand and respond to legitimacy concerns can endanger both the courts and the law they interpret and apply.