18. This power, known as the principle of "Kompetenz-Kompetenz" in German or "la compétence de la compétence" in French, is part, and indeed a major part, of the incidental or inherent jurisdiction of any judicial or arbitral tribunal, consisting of its "jurisdiction to determine its own jurisdiction." It is a necessary component in the exercise of the judicial function and does not need to be expressly provided for in the constitutive documents of those tribunals, although this is often done (see, e.g., Statute of the International Court of Justice, Art. 36, para. 6). But in the words of the International Court of Justice:

"[T]his principle, which is accepted by the general international law in the matter of arbitration, assumes particular force when the international tribunal is no longer an arbitral tribunal […] but is an institution which has been pre-established by an international instrument defining its jurisdiction and regulating its operation." (Nottebohm Case (Liech. v. Guat.), 1953 I.C.J. Reports 7, 119 (21 March).)

This is not merely a power in the hands of the tribunal. In international law, where there is no integrated judicial system and where every judicial or arbitral organ needs a specific constitutive instrument defining its jurisdiction, "the first obligation of the Court - as of any other judicial body - is to ascertain its own competence." (Judge Cordova, dissenting opinion, advisory opinion on Judgements of the Administrative Tribunal of the I.L.O. upon complaints made against the U.N.E.S.C.O., 1956 I.C.J. Reports, 77, 163 (Advisory Opinion of 23 October)(Cordova, J., dissenting).)

[…]

22. In conclusion, the Appeals Chamber finds that the International Tribunal has jurisdiction to examine the plea against its jurisdiction based on the invalidity of its establishment by the Security Council.