Earlier this year, the European Union, the Council of Europe, Ukraine and an international coalition of states agreed to establish a new special tribunal.The tribunal will eventually be tasked with holding Russia accountable for the 2022 full-scale invasion of Ukraine. It’s expected to start operating in 2026. Human rights organisations, international lawyers and some (mostly European) states have long been calling for the establishment of such a tribunal. Oleksandra Matviichuk, a Ukrainian human rights lawyer, called the establishment of the tribunal:an important breakthrough for the international justice community and especially for the millions of Ukrainians who have been harmed by the Russian aggression.However, important questions remain about if it could truly hold senior Russian officials accountable.So, how will this new special tribunal work, and will it be effective – or necessary?How does the special tribunal fill the gaps left by the ICC and ICJ?This tribunal is separate to the International Criminal Court (ICC) and the International Court of Justice (ICJ). The ICC can prosecute individuals charged with genocide, war crimes and crimes against humanity in the Russian war on Ukraine. So far, it has issued arrest warrants against four Russian senior officials, including President Vladimir Putin.Because Russia is not a member state to the court, the court can’t exercise legal authority over what’s known in international law as a crime of aggression (when leaders of a state launch or plan a war). For the ICC to be able to exercise this jurisdiction, the aggressor state also must be a member state of the court. The ICJ is a different court altogether. It primarily deals with and adjudicates disputes between states, not limited to war crimes, crimes against humanity and genocide. It can’t hold individuals accountable, and can only exercise jurisdiction over a dispute if both states to a dispute agree. While the ICC seeks to establish individual criminal responsibility, the ICJ may establish state responsibility for a violation of international law.Currently, there are also two cases between Ukraine and Russia before the ICJ. Neither deals with the question of the legality of Russia’s use of force in its invasion in February 2022. Both Ukraine and Russia would need to consent to bring this issue before the court.So, is a new tribunal necessary?Yes, because the crime of aggression currently can’t be addressed by any other international court or tribunal.Given the limitations of what the ICJ and ICC can do, a dedicated tribunal seems the obvious solution to hold those responsible for the illegal use of force against Ukraine accountable. And it’s not uncommon for specialised tribunals with limited jurisdiction over a specific situation to be created. Other historical examples include the International Criminal Tribunal for the former Yugoslavia, the International Criminal Tribunal for Rwanda, the Extraordinary Chambers in the Courts of Cambodia and the Special Court for Sierra Leone.Given the ICC’s lack of jurisdiction over the crime of aggression, the new special tribunal would complement the court’s existing investigations into war crimes and crimes against humanity.Who is running the new tribunal and how will it work?The exact content and specifics of this new tribunal will remain unknown until the draft statute of the tribunal is published. That’s a document that outlines details including the tribunal’s jurisdiction, the applicable definition of aggression and how the tribunal will function.At this stage, the Council of Europe has confirmed the tribunal will work within its legal framework and principles. It will be funded by an international coalition of supportive states. A management committee of members and associate members of the tribunal will be responsible for the election of the tribunal’s judges and prosecutors. The management committee is made up of the Council of Europe’s council of ministers and Ukraine.Diplomatic discussions are still ongoing at this point, but the legal process for establishing the special tribunal can begin now.Will this special tribunal be more effective?Political, legal and practical challenges for the special tribunal remain. It’s unclear if the most senior Russian state officials can and will be able to be brought to trial for the crime of aggression.Nothing, so far, suggests the statute of the tribunal will contain an exception to state immunity enjoyed by heads of state, heads of governments and foreign ministers while in power. That means these office holders can only be prosecuted if they are no longer in power or the Russian government expressly waives their immunity. It’s also unclear whether states will be willing to arrest those sought by the special tribunal.The ICC has long faced this challenge trying to get states to act on its arrest warrants. Hungary, for instance, did not arrest Israel’s Prime Minister Benjamin Netanyahu when he visited in April, despite an ICC arrest warrant for alleged crimes against humanity in connection with the war in Gaza. For the special tribunal to be effective, according to Oleksandra Matviichuk, it:must not become a remote and hollow entity that does not engage with the Ukrainian victims.Overall, much remains unclear. Will this new special tribunal be able to hold the likes of Putin accountable for the crime of aggression? Or will it become another empty promise?Yvonne Breitwieser-Faria does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.