Abstract: The decision on jurisdiction in the ICSID case Abaclat vs. Argentina may be rightfully included in the gallery of controversial decision and awards of arbitral tribunals dealing with investment disputes. The dispute is one of the many arising out of the financial crisis in Argentina in 2001-2002 and it concerns Argentina's failure to pay the bonds acquired by Italian investors. This is the first case where the tribunal had to decide whether the ICSID Convention allows submission of collective claims on behalf of 60,000 investors. The tribunal also had the difficult mission to settle the debate over the nature of sovereign debts and their qualification as investments for the purpose of the ICSID Convention. The Decision on Jurisdiction was taken by the majority, while the third arbitrator, after issuing his dissenting opinion, has resigned. The costs incurred by the parties to reach this stage of the proceedings might also be a record for the ICSID: US$ 35 million.