The book is an evaluation of the doctrine and practice of international criminal courts and tribunals on the position of witnesses against a theoretically informed ideal of a cosmopolitan world order. It seeks to ascertain that there is a cosmopolitan international community, with shared values, that are instantiated in the international criminal tribunals, and that is what justifies the exercise of jurisdiction over witnesses who provide false testimony or engage in other forms of contempt of court. The book evaluates the practice of the International Criminal Court (ICC), the International Criminal Tribunal for the former Yugoslavia, the International Criminal Tribunal for Rwanda and the Special Court for Sierra Leone.