See also Fed. R. Civ. P. 23 and all its subcategories. One or more members of a class of persons may sue or be sued as representatives of the entire class. A class action is generally permitted if necessity or convenience justify actions on behalf of the group as opposed to multiple suits by the class members being filed and prosecuted. Under federal law (1) the class must be so large that individual suits would be impracticable, (2) there must be legal or factual questions common to the class, (3) the claims or defenses of the representative parties must be typical of those of the class, and (4) the representative parties must adequately protect the interests of the class. Fed. R. Civ. P. 23.
The justifications for class action lawsuits was set forth in Justice Mosk's oft-quoted majority opinion in Vasquez v. Superior Court (1971) 4 Cal.3d 800, 808 [94 Cal. Rptr. 796, 484 P.2d 964] (Vasquez): 'Frequently numerous consumers are exposed to the same dubious practice by the same seller so that proof of the prevalence of the practice as to one consumer would provide proof for all. Individual actions by each of the defrauded consumers ...