Black-letter propositions
- 01
Rule 23(a) requires a sufficiently numerous class, common contentions capable of classwide resolution, typical representative claims, and adequate representatives and counsel.
- 02
A 23(b)(3) damages class also requires predominance and superiority, mandatory best-practicable notice, and opt-out rights.
- 03
Injury and Article III standing remain necessary; certification does not expand substantive rights.
- 04
For statutory diversity under CAFA, minimal diversity, at least 100 members, and an aggregate amount over $5 million generally suffice, subject to exceptions.
Use this attack sequence under time
Frame the issue
Define the proposed class and representative.
Resolve the next checkpoint
Apply all four Rule 23(a) prerequisites.
Resolve the next checkpoint
Choose the exact Rule 23(b) route.
Finish the conclusion
Address notice, opt-out rights, manageability, and jurisdiction.
Common wrong turns
- Many similar claims do not automatically establish a common answer.
- A settlement class still must satisfy certification requirements.
- Ordinary diversity class actions and CAFA use different jurisdictional rules.
Worked example
Thousands of buyers allege the same mislabeled fee, but each signed a materially different contract.
Numerosity is clear, but commonality and especially predominance depend on whether liability can be resolved through shared proof despite contract variation. The court must analyze the proposed class, not assume aggregation.
Practice this topic
Rule 23's requirements
Rule 23(a) allows one or more class members to sue or be sued as representative parties only if the class is so numerous that joinder of all members is impracticable, there are common questions of law or fact, the representatives' claims or defenses are typical of the class, and the representatives will fairly and adequately protect the class's interests.
Rule 23(b) then requires one of three types. The first is a risk of inconsistent adjudications or of adjudications dispositive of other members' interests. The second is the opposing party acting on grounds that apply generally to the class so injunctive or declaratory relief is appropriate. The third requires that common questions predominate over individual questions and a class action be superior to other methods.
Certification and the federal statute
Rule 23(c)(1) requires the court, at an early practicable time, to determine by order whether to certify the class, and an order certifying a class must define the class and appoint class counsel. For predominance and superiority, Rule 23(b)(3) lists matters pertinent to the findings, including members' interests in controlling separate actions, existing litigation, the desirability of concentrating the litigation in the forum, and difficulties in managing the class.
28 U.S.C. 1332(d) contains separate jurisdictional requirements for class actions, so the amount and diversity analysis for a class differs from the ordinary rule.
Frequently asked questions
What is the controlling rule for class actions?+
A class may be certified only when Rule 23(a) and one Rule 23(b) category are proved with evidence and the court addresses the applicable notice and opt-out protections.
How should I analyze class actions on the bar exam?+
Define the proposed class and representative. Apply all four Rule 23(a) prerequisites. Choose the exact Rule 23(b) route. Address notice, opt-out rights, manageability, and jurisdiction.
What are the Rule 23(a) prerequisites?+
Numerosity, commonality, typicality and adequacy of representation, all four of which must be satisfied before a class can be maintained under Rule 23(b).
What are the three types of class action under Rule 23(b)?+
Risk of inconsistent or dispositive adjudications, generally applicable conduct supporting injunctive or declaratory relief, and predominance of common questions with superiority of the class device.
What must the court decide about certification?+
Whether to certify the action at an early practicable time, by order that defines the class and appoints class counsel, under Rule 23(c)(1).
What does predominance require?+
That questions of law or fact common to class members predominate over questions affecting only individual members, under Rule 23(b)(3).