State immunity is also known as sovereign immunity, reflecting its origins in the sanctity of kingship. State immunity may be pleaded by a foreign state when a person wishes to make it a party to legal proceedings in the court of another state, usually as the defendant. If successful, the plea prevents the court from exercising jurisdiction over the state, provided of course that it has jurisdiction in the particular case. The dispute can then be disposed of only by the courts of the foreign state itself, by an international court or tribunal or by diplomatic settlement. Originally, state immunity was absolute, and remained so into modern times even though states were then carrying out many commercial transactions abroad. It was not until the second half of the twentieth century that a restrictive approach – removing immunity for commercial matters – came to be generally accepted.
State immunity is a doctrine of customary international law. But unlike the law of state responsibility, which has been developed almost entirely by international courts and tribunals, state immunity is much more the product of judgments of domestic courts. Their approaches to state immunity reflect differences between their legal, political and economic systems. But, in recent decades, there has been more convergence in domestic legislation and judgments, so that it is now easier to describe the law of state immunity. This is now helped by the UN General Assembly’s adoption on 2 December 2004 of the UN Convention on the Jurisdictional Immunities of States and Their Property (in this chapter, the ‘UN Convention’). The (integral) annex to the Convention contains ‘Understandings’ with respect to certain of its provisions. The Convention does not apply to questions of immunity involving states or their property arising in proceedings instituted before its entry into force (after thirty ratifications), except insofar as it reflects customary international law. But, even before then, the Convention may well influence domestic courts who will by their judgments still develop the law. Therefore, the best advice one can give to anyone with a claim against a foreign state, or indeed the state itself, is to instruct lawyers who really are expert in the local law on state immunity. But first we must distinguish state immunity from other related subjects.