On May 22, 2025, the Council of the European Union formally adopted the United Nations Convention on Transparency in Treaty-based Investor-State Arbitration (the Mauritius Convention), marking a significant step toward promoting public accountability in investor–state arbitration. Developed under the auspices of UNCITRAL, the Mauritius Convention provides transparency obligations in arbitration proceedings between foreign investors and states, including publication of documents, open hearings, and third-party submissions. EU member states are now expected to ratify the Mauritius Convention, further consolidating the EU’s stance in favour of procedural openness in investor–state dispute settlement.