On September 16, 2015, the U.S. Court of Appeals for the Second Circuit (Court) overruled [3] a lower court’s class definition in a class action suit brought by bondholders against Argentina.  The case arose out of litigation by bondholders seeking repayment after Argentina’s default on its sovereign debt in 2001. The lower court’s decision in this instance had “simply [modified] the class definition by removing the continuous holder requirement and expanding the class to all holders of beneficial interests in the relevant bond series without limitation as to time held.” The Court stated that Rule 23 of the Federal Rules of Civil Procedure [4] implied a “requirement of ascertainability,” which requires the class to be “sufficiently definite so that it is administratively feasible for the court to determine whether a particular individual is a member.” It rejected the argument that use of any objective criteria is sufficient to define a class “when those criteria, taken together, do not establish the definite boundaries of a readily identifiable class.” According to the Court, the present case falls into this category, because the “objective standard—owning a beneficial interest in a bond series” would not allow definite identification of the class members. Argentine bonds are still actively traded on the market, all using the same trading number identifier. The Court concluded that “[t]he features of the bonds in this case thus make the modified class insufficiently definite as a matter of law.”