State immunity is highly unusual among established areas of public international law in that it has been created and developed largely through cases in national courts and through national legislation. In sharp contrast to diplomatic and consular privileges and immunities, the role of reciprocity and of diplomatic negotiation in shaping the rules of state immunity has been rather limited. While national courts have purported to apply these rules as international law, they have inevitably viewed them within the frame-work of the constitutional approach taken by the particular national legal order to rules of international law and they have looked to earlier national precedents rather than to cases in other jurisdictions. In consequence, cross-fertilization has been rather limited and the process of response by national courts to the changing functions of States in the modern world has been painfully slow. Over the past 30 years, the uncertainties and inadequacies of leaving state immunity rules to national courts has been addressed mainly through national statutes—but while the draftsmen and legislators have paid careful attention to other statutes and tried to follow their best features, this process has compounded the perception of the courts that state immunity is an area of national law, to be interpreted and refined at national level.