It is often claimed that, under customary international law, immunity ratione materiae can be refused in domestic criminal proceedings regarding ce11ain egregious crimes. I label this the 'Qualified Interpretation of immunity ratione materiae.' I ask whether this claim is true and, if it is, which crimes it applies to. While the Qualified Interpretation gained prominence after Pinochet, the stock arguments for the claim appear unconvincing. More recent decisions such as the Arrest Warrant Case, Italy v Germany and Jones v UK cast further doubts. In pm1icular, it has been found that, in civil proceedings, immunity ratione materiae covers all conduct for which the State would be immune if sued directly, including violations of jus cogens norms. Nonetheless, I argue that a narrow version of the Qualified Interpretation, applying specifically in criminal proceedings regarding international crimes, can be defended. In order to do so, however, it is necessary to re-examine the underlying rules and rationales for immunity ratione materiae. Three distinct rules are identified: i) The Non-Circumvention' rule: Litigants must not sue individual State officials as a means of indirectly accessing State funds. ii) The 'Exclusive-Attribution' rule: Acts performed on behalf of the State cannot generally be attributed to individual officials. iii) The 'Treaty-Based' rule of immunity ratione materiae: Host States must not exercise jurisdiction over consular personnel or former diplomatic agents with regard to acts performed in exercise of the specific functions listed in the VCCR and VCDR respectively. I argue that the first rule applies in civil proceedings even with regard to violations of jus cogens norms but does not apply in criminal proceedings. The second is subject to a customary international law exception regarding all crimes for which international law imposes individual criminal responsibility. The third is subject to a treaty-based exception regarding acts that violate international law