Immunity serves to stay (stop or freeze) the jurisdiction of national courts. It is a procedural bar to their ordinary jurisdiction, not a substantive bar. This means that it stops the courts from actually hearing the case, not that the substance of the claim is no longer valid. As a result, if and when the immunity is subsequently lifted in the future, the claim may be brought before a court once again.

A distinction is made between State (or sovereign) immunity and diplomatic and consular immunities. The first concerns States as such (covering both acts and persons) whereas the latter concerns the personal immunities of a State’s representatives and State assets abroad.

The international law of immunity is primarily found in customary international law in the form of domestic legislation and decisions of national courts. The International Court of Justice (ICJ) has also issued judgments that have fundamentally shaped the law in this area. There is also a small body of treaties that are largely devoted to diplomatic and consular immunities, as well as general jurisdictional immunities of States.

Immunity from the jurisdiction of national courts should be distinguished from the ordinary jurisdiction of international courts and tribunals. The jurisdiction of international courts is derived from their statutes, not from customary international law or from treaties dealing with immunities. Therefore, immunity before international tribunals may be completely different to immunity under treaty and customary international law.

Immunities should not be confused with amnesties. The former are afforded by the laws and courts of foreign nations, whereas amnesties are granted by the home country of the accused. Unlike immunities, an amnesty constitutes a substantive bar to the prosecution of an accused person because amnesty laws forgive the perpetrator for the actual crime he or she committed.