Class Certification

Class certification is the procedural gateway that transforms an individual lawsuit into a class action, allowing one or more named plaintiffs to litigate on behalf of a larger group with shared legal or factual claims. In U.S. federal practice, certification is governed by Rule 23 of the Federal Rules of Civil Procedure. Plaintiffs must satisfy the four prerequisites of Rule 23(a) — numerosity, commonality, typicality, and adequacy of representation — and then fit the case into one of the categories in Rule 23(b), most commonly Rule 23(b)(3), which requires that common questions predominate over individual ones and that a class action be superior to other methods of adjudication.

The certification decision is often outcome-determinative: denial typically ends the litigation as a practical matter, while certification creates significant settlement pressure on defendants. Because of these stakes, Rule 23(f) permits interlocutory appeal of certification rulings at the appellate court's discretion.

The U.S. Supreme Court has tightened certification standards in several rulings. In Wal-Mart Stores, Inc. v. Dukes (2011), the Court decertified a nationwide sex-discrimination class of roughly 1.5 million female employees, holding that the plaintiffs failed to show a common question capable of class-wide resolution. In Comcast Corp. v. Behrend (2013), the Court emphasized that damages models must be tied to the plaintiffs' theory of liability at the certification stage. Amchem Products, Inc. v. Windsor (1997) earlier rejected a sprawling asbestos settlement class for failing predominance and adequacy.

Class actions exist in many jurisdictions beyond the United States, though under different labels and standards — for example, Group Litigation Orders in England and Wales, recours collectif in Quebec, and collective redress mechanisms expanded across the EU under Directive (EU) 2020/1828 on representative actions for consumers. Certification-equivalent screening exists in most of these systems, though the criteria and opt-in/opt-out defaults vary substantially.