A class action is a lawsuit wherein an entire group (class) of claimants is the plaintiff. This device affords large numbers of people with a common interest in a matter the opportunity to seek redress for a grievance through one legal action. Often, persons qualifying for participation in the class do not know they have the right to bring an action, or, even if they know, do not have the wherewithal to do so separately.

The class action is regarded as a convenient and efficient vehicle for resolving legal disputes affecting a number of parties with similar claims so that the common issues that could have similar outcomes do not have to be tried piecemeal in separate actions, thus saving the courts and the litigants time and money.

Under prevailing law unnamed parties to a class action are bound by the final judgment in the action so long as their interests were adequately represented.

A class action may be brought in either the state or federal court system. Most states pattern their rules after the Federal Rules of Civil Procedure which defines three kinds of class actions. The first type may be brought where separate lawsuits might adversely affect other members of the class or the defendant in either of two ways—if the piecemeal litigation resulting from separate suits might impose inconsistent standards of conduct on the defendant, or if multiple suits might "impair or impede" the class members from protecting their various interests. In the second type of class action, a class seeks an injunction or some type of relief compelling the defendant either to cease a certain activity or to perform some other type of action. In the third category of class action lawsuit, there are questions of law or fact common to the entire class that predominate over questions peculiar to each individual plaintiff, and a class action suit is a more efficient means to resolve the controversy. Under the third type of class action, individual members of the class may "opt out" of the litigation if they do not want to be bound by the results of the suit. Courts have held that due process requires that absent class members be given adequate notice, adequate representation, and adequate opportunity to opt out, before they can be bound by a final

Class actions have a significant social purpose. A lawyer who prosecutes a class action can be viewed as a "private attorney general" who aggressively enforces various regulatory laws or who alerts the public to fraud, health, and safety problems. In a time when government is seeking to reduce government regulation, class action lawsuits provide an opportunity for the private sector to take up the oversight function.

The class action format has most often been used to aggregate small claims that were not worth litigating separately. A class action is an effective means for holding defendants accountable for widespread harm that would otherwise go unchecked. There is public value in allowing this type of class action to go forward, even if the amount payable to each member of the class is small. The deterrent effect of a class action can be substantial, forcing the defendant to change its product or procedures.