Class certification is an unique procedural step for class actions. For a certain class to be certified, the class shoud satisfy all the requirements Federal Rules of Civil Procedure Rule 23 (a) and (d) set. Rule 23(a) calls for numerosity, commonality, typicality, and adequacy of representation. Rule 23(b) devides class actions into three category and demands different requirements according to specific type of class actions. Because of these requirements class certification functions as a gate keeper to filter out lawsuits not suitable for a class action format; and sets grounds for a class action to proceed. In addition, once certified, the class action is more likely to be disposed through settlement due to settlement pressure to the defendnat and other reasons. In Dukes v. Wal-Mart stores, 5-4 decision that denied class certification for a proposed class, the majority opinion established a new standard for a commonality requirement. The new standard substatially considers strength of merits of the claim under the name of ``rigorous analysis``; and focuses significantly on dissimilarities among class members. This case has numerous implications including: 1) the ``dissimilarities approach`` of the majority opinion is doubtful when considering languages of Rule 23(b)(2) and (b)(3); 2) the decision manifests the Robert Court`s strong willingness to regulate frivolous lawsuits using stricter standards; 3) the new standard would practically bar class actions that has ``too big`` classes; 4) the decision undermines case law that had prohibited consideration of merits.