Most New Jersey litigators and first-year law students are generally familiar with the four threshold requirements for class action certification under Federal Rule of Civil Procedure 23: numerosity, commonality, typicality, and adequacy (or adequate representation). Most are also familiar with the relatively recent development of the requirement that a class be ascertainable. Ascertainability generally requires that members of a proposed class be readily identifiable through objective criteria, and that administratively feasible method exists for identifying class members and determining class membership. Courts and scholars have both praised and criticized the ascertainability doctrine, resulting in contrasting opinions and approaches even here in New Jersey. Indeed, the requirement of ascertainability in New Jersey state and federal courts differs significantly, and lawyers must be aware of these differences when litigating class action claims.