---
title: "Class Action Requirements (Rule 23)"
type: Legal Rule
source: https://casebriefly.com/legal-rules/class-action-requirements-rule-23
---

# Class Action Requirements (Rule 23)

Federal Rule 23 permits representative litigation on behalf of a class when numerosity, commonality, typicality, and adequacy of representation are established, and the action fits one of three categories: prejudice, injunctive relief, or predominance of common questions.

## Definition

Federal Rule of Civil Procedure 23 governs class actions, which allow one or more named representatives to litigate on behalf of a class of similarly situated persons. A class action must satisfy four prerequisites under Rule 23(a): numerosity (the class is so numerous that joinder of all members is impracticable), commonality (there are questions of law or fact common to the class), typicality (the claims or defenses of the representative parties are typical of the class), and adequacy of representation (the representatives will fairly and adequately protect the interests of the class).

In addition to the Rule 23(a) prerequisites, the action must fit within one of three categories under Rule 23(b). Rule 23(b)(1) applies when separate actions would create a risk of inconsistent adjudications or would practically dispose of the interests of absent members. Rule 23(b)(2) applies when the opposing party has acted or refused to act on grounds generally applicable to the class, making injunctive or declaratory relief appropriate for the class as a whole. Rule 23(b)(3) applies when common questions of law or fact predominate over individual questions and a class action is superior to other methods of adjudication; this is the most common type and requires notice and opt-out rights.

The Supreme Court in Wal-Mart Stores, Inc. v. Dukes (2011) heightened the commonality standard, requiring that the class demonstrate a common contention capable of classwide resolution whose determination will resolve a central issue in one stroke. In Comcast Corp. v. Behrend (2013), the Court tightened predominance by requiring that damages be susceptible to measurement on a classwide basis. Courts must conduct a rigorous analysis of the Rule 23 requirements at the certification stage, even if that analysis overlaps with the merits.

## Elements

- Numerosity: the class is so numerous that joinder of all members is impracticable
- Commonality: questions of law or fact common to the class (Wal-Mart heightened standard)
- Typicality: the representative's claims are typical of the class
- Adequacy: the representative will fairly and adequately protect the class's interests
- The action must satisfy one of Rule 23(b)(1), (b)(2), or (b)(3)
- Rule 23(b)(3) requires predominance of common questions and superiority of the class action device
- Rigorous analysis is required at the certification stage

## Key Case

Wal-Mart Stores, Inc. v. Dukes, 564 U.S. 338 (2011)

## Landmark Cases

| Name | Citation | Significance |
| --- | --- | --- |
| Wal-Mart Stores, Inc. v. Dukes | 564 U.S. 338 (2011) | Heightened the commonality requirement, holding that the class must demonstrate common contentions capable of classwide resolution, not merely common questions. |
| Amchem Products, Inc. v. Windsor | 521 U.S. 591 (1997) | Held that settlement classes must independently satisfy Rule 23 requirements, including predominance and superiority under Rule 23(b)(3). |
| Comcast Corp. v. Behrend | 569 U.S. 27 (2013) | Held that predominance requires that damages be measurable on a classwide basis consistent with the liability theory. |
| Phillips Petroleum Co. v. Shutts | 472 U.S. 797 (1985) | Established due process requirements for class actions binding absent members, including notice, opt-out rights, and adequate representation. |
| Tyson Foods, Inc. v. Bouaphakeo | 577 U.S. 442 (2016) | Held that representative evidence (statistical sampling) can be used to prove classwide liability, provided the evidence is admissible and could sustain a reasonable jury finding for each class member. |

## Exam Tips

- Analyze each Rule 23(a) prerequisite separately and explicitly. Then determine which Rule 23(b) category applies. Most exam questions focus on (b)(3) predominance and superiority.
- After Wal-Mart v. Dukes, commonality is more rigorous than it sounds. The class must identify a common contention whose resolution will drive the litigation.
- For Rule 23(b)(3), distinguish predominance (common questions must outweigh individual ones) from the commonality requirement in Rule 23(a) (at least one common question).
- Remember that Rule 23(b)(3) classes require opt-out notice to absent members, while (b)(1) and (b)(2) classes generally do not.

## Common Mistakes

- Treating commonality under Rule 23(a) as a low bar after Wal-Mart v. Dukes; the standard now requires common contentions capable of generating common answers.
- Confusing the commonality requirement of Rule 23(a) with the more demanding predominance requirement of Rule 23(b)(3).
- Forgetting that class certification requires a rigorous analysis that may overlap with the merits, and that the court must resolve any factual disputes relevant to certification.

## Mnemonic Or Memory Aid

Rule 23(a) prerequisites: CANT = Commonality, Adequacy, Numerosity, Typicality. Then fit into (b)(1), (b)(2), or (b)(3).

## Related Rules

- joinder-of-parties-rule-20
- intervention-rule-24
- claim-preclusion-res-judicata
- supplemental-jurisdiction

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Source: [Class Action Requirements (Rule 23) — CaseBriefly](https://casebriefly.com/legal-rules/class-action-requirements-rule-23)