Glossary · Class Action Basics

Class Certification: The Rule 23 Test, Explained

By Steve Levine · Updated June 19, 2026 · 7 min read

Quick Answer

Class certification is the court order that turns a lawsuit filed by a few named plaintiffs into a case that proceeds on behalf of a whole group — the "class." Under Federal Rule of Civil Procedure 23, the judge has to find the class is numerous, shares common questions, is fairly represented by typical and adequate plaintiffs, and (for the usual money-damages class) that common issues predominate and a class action is the superior way to resolve the dispute. It is the make-or-break moment: certify, and the case has the leverage to win class-wide relief or drive a settlement; deny, and there is usually nothing for the rest of the class to claim.

What Class Certification Is

A class action starts as an ordinary lawsuit filed by one or a few people — the named plaintiffs, or class representatives. It does not actually become a case on behalf of thousands (or millions) of others until a judge says it can. That decision is class certification: a court order under Federal Rule of Civil Procedure 23 finding that the dispute is suitable to be litigated collectively, defining exactly who is in the group, and appointing the lawyers who will represent it.

Certification is not a ruling on whether the defendant did anything wrong. The court is deciding the structure of the case, not the merits — though in practice it often looks closely at the evidence to decide whether the case can really be tried on a class-wide basis. The plaintiffs file a motion for class certification, both sides brief it (usually with dueling expert reports), and the court rules. A grant or denial of certification can be appealed immediately under Rule 23(f), which is unusual — most pretrial rulings have to wait until the end of the case.

The Rule 23 Factors

To certify a class, the court works through a two-part test. First, all four requirements of Rule 23(a) must be met. Then the case must fit into one of the categories in Rule 23(b) — most consumer money cases proceed under Rule 23(b)(3), which adds two more requirements.

Numerosity The class is so large that suing individually, or joining everyone into one normal lawsuit, would be impractical. There is no magic number, but classes in the dozens are often enough and classes in the hundreds or thousands easily qualify.
Commonality There is at least one question of law or fact common to the whole class — for example, whether a standard contract term was unlawful, or whether a product had the same defect. The answer must be capable of resolving an issue for everyone at once.
Typicality The named plaintiffs' claims arise from the same conduct and legal theory as the rest of the class. Their situation has to be representative, not a special case that turns on facts unique to them.
Adequacy The class representatives and their lawyers (class counsel) will fairly and vigorously protect the interests of absent class members, with no disabling conflicts between the representatives and the group.
Predominance (23(b)(3)) The common questions outweigh the questions that would have to be decided person-by-person. If every class member's claim turns on individualized proof, predominance fails.
Superiority (23(b)(3)) A class action is a better way to resolve the dispute than thousands of separate suits — typically true when each individual claim is too small to litigate alone.
Other types of classes exist. Rule 23(b)(2) covers cases seeking injunctive or declaratory relief for the whole group (civil-rights and policy-change cases), and Rule 23(b)(1) covers situations where separate suits would create incompatible obligations or impair other members' interests. Those categories do not require predominance or superiority, and 23(b)(2) classes generally do not carry opt-out rights.

Litigation Class vs. Settlement Class

The same Rule 23 test is applied in two very different settings.

• Litigation class. Certified so the case can actually be tried as a class action. Here the plaintiffs have to satisfy every factor in full, including showing the trial would be manageable — that the court could realistically try the common issues without it collapsing into thousands of mini-trials.
• Settlement class. Certified only to carry out a settlement the parties have already agreed to. Because there will be no trial, the court does not evaluate trial manageability. But the other protections still apply, and courts scrutinize settlement classes carefully to make sure the deal is fair before granting preliminary approval.

That is why you will often see a class "certified for settlement purposes only." It means the group was approved so a settlement could be distributed — not that a court ever found the case triable as a class.

Class Definition, Class Period, and Subclasses

Certification fixes the exact boundaries of who is covered. Three pieces matter most:

• Class definition. The precise description of who is in and who is out — for instance, "all U.S. residents who purchased Product X between two dates." A class has to be defined by objective criteria so membership can be determined without a mini-trial for each person.
• Class period. The window of dates that qualify. Buy the product a day after the class period ends and you are not a member, no matter how similar your situation.
• Subclasses. When different segments have different claims or damages — say, California purchasers with a state-law claim versus the nationwide group — the court may divide the class into subclasses, each with its own representative, so no segment's interests are sacrificed for another's.

These boundaries are exactly what to check when a settlement is announced: read the class definition and class period to see whether you actually qualify.

Why Certification Decides the Case

Class certification is widely considered the single most important ruling in a class action — often more decisive than the eventual verdict. The reason is leverage. Individually, most consumer claims are worth too little to litigate; aggregated across a certified class, the same claims can expose a defendant to enormous liability. So a grant of certification dramatically raises the pressure to settle, while a denial frequently ends the case as a practical matter — the named plaintiffs are left with only their own small claims.

Because the stakes are so high, certification is heavily litigated, and provisional certification is also one of the things the court addresses at preliminary approval of a settlement. Certification is likewise the moment class members' opt-out rights attach in a damages class — the point at which absent members must be told about the case and given a chance to exclude themselves.

What It Means for You

If you fall within a certified class, here is the practical picture:

• You are usually in automatically. In a Rule 23(b)(3) damages class you are a member by default and bound by the result unless you opt out by the deadline in the class notice.
• Certification is not a payday. It means the case can proceed as a class — not that money exists yet. A fund to pay from typically arrives much later, through a settlement or judgment, with its own claim form and deadline.
• Read the class definition. Whether you qualify turns entirely on the class definition and class period — not on how similar your experience feels.
• Watch the notice. If you want to keep your right to sue on your own, the certification notice is where the opt-out deadline lives.

Frequently Asked Questions

What is class certification in a class action?

Class certification is the court order deciding that a lawsuit can proceed on behalf of a defined group of people (the class) rather than only the named plaintiffs. Under Federal Rule of Civil Procedure 23, the judge must find numerosity, commonality, typicality, and adequacy of representation, and — for a typical money-damages class — that common questions predominate and that a class action is the superior way to resolve the dispute. Without certification, there is no class and no class-wide recovery.

What are the Rule 23 requirements for certifying a class?

Rule 23(a) requires four things: numerosity (the class is too large to join everyone individually), commonality (there are questions of law or fact common to the class), typicality (the named plaintiffs' claims are typical of the class), and adequacy (the representatives and their lawyers will fairly protect the class). For the most common type of damages class under Rule 23(b)(3), the court must also find predominance (common questions outweigh individual ones) and superiority (a class action is better than other ways of handling the dispute).

What is the difference between a litigation class and a settlement class?

A litigation class is certified so the case can be tried as a class action; the plaintiffs must fully satisfy every Rule 23 factor, including showing the case is manageable as a trial. A settlement class is certified only to carry out an agreed settlement, so the court does not assess trial manageability. Both still require the court to protect class members through an adequate class definition, fair notice, and a fair distribution plan.

What happens if a class is not certified?

If the court denies class certification, the case does not end, but it can no longer move forward on behalf of the group. The named plaintiffs may continue with only their own individual claims, appeal the denial, or amend and try again with a narrower class definition. For everyone else in the proposed class, a denial usually means there is nothing to claim — there is no class-wide recovery unless and until a class is certified.

Do I need to do anything when a class is certified?

Usually not right away. When a damages class is certified, the court orders notice to class members explaining their rights, including the deadline to opt out (exclude themselves). If you do nothing, you typically remain in the class and are bound by the outcome. You generally do not file a claim form until a settlement or judgment creates a fund to pay from, which often comes much later.


Related Terms

About This Page

General legal-process information, not legal advice. OpenClassActions.com is a consumer news site and is not a law firm or a settlement administrator. The requirements for certifying a class vary by jurisdiction and by the specific facts of each case; the governing rule and the court's order control in any individual lawsuit.

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