What is class certification?

When a lead plaintiff files a class action, the complaint describes a proposed class, such as "all persons in the United States who paid a late fee to the company since January 1, 2022." At that stage, only the named plaintiffs are actually parties. The certification order changes that.

Under Rule 23(c)(1), the court must decide whether to certify the class "at an early practicable time," and an order certifying a class must define the class and its claims and appoint class counsel under Rule 23(g). Once certified, the case proceeds for every member, and the eventual judgment or settlement binds everyone who did not opt out.

Certification also triggers notice. For damages classes, class members get notice explaining the case and their right to request exclusion. See rights of a class member for what that notice must include.

Every federal class must satisfy four prerequisites, often shortened to numerosity, commonality, typicality, and adequacy:

Numerosity has no fixed number. The Supreme Court said in General Telephone Co. v. EEOC (1980) that the requirement "imposes no absolute limitations" and depends on each case's facts. The Second Circuit has said numerosity is presumed at a level of 40 members, and many courts use similar rules of thumb. Our guide on how many people you need for a class action covers this in detail.

Commonality became harder to prove after Wal-Mart Stores, Inc. v. Dukes, decided June 20, 2011. The Court reversed certification of a class of about 1.5 million female employees, holding that the claims had to depend on a common question whose answer would resolve an issue central to every member's claim, not just a shared allegation of discrimination by thousands of different managers.

After meeting Rule 23(a), a class must fit one of three categories in Rule 23(b):

• Rule 23(b)(1): separate lawsuits would risk inconsistent rulings or would, as a practical matter, decide other people's interests. This is used for limited funds and similar situations.
• Rule 23(b)(2): the defendant acted on grounds that apply generally to the class, so a court order (an injunction or declaration) is appropriate for everyone. Civil rights and policy challenges often use this type. See what injunctive relief is.
• Rule 23(b)(3): common questions predominate over individual ones, and a class action is superior to other methods. This is the category for nearly all consumer cases seeking money.

Predominance is where most damages classes are won or lost. If the company can show that deciding each person's claim would require individual proof, such as what each buyer was told, whether each person relied on an ad, or how much each person was harmed, the court may refuse to certify. Data breach, fee, and statutory damages cases, where the conduct was uniform, tend to certify more readily than injury or fraud cases. In Amchem Products, Inc. v. Windsor (1997), the Supreme Court refused to certify a nationwide asbestos settlement class because class members' exposures and illnesses differed too much for common issues to predominate.

A certification ruling is not necessarily the last word. Under Rule 23(f), a party may petition the court of appeals for permission to appeal a certification order within 14 days after it is entered (45 days if the United States is a party). The appeals court can decline to hear it, and an appeal does not pause the case unless a judge orders it.

The trial court can also change its mind. Rule 23(c)(1)(C) lets the court alter or amend a certification order before final judgment, which is how classes are sometimes decertified after discovery reveals more individual differences than expected.

Many classes are certified only for settlement. When the parties reach a deal before a contested ruling, they ask the judge to certify a settlement class at the same time the deal is approved. Under Rule 23(e), notice goes out only if the court finds it will likely be able to approve the proposal and certify the class for purposes of judgment on it. Most of the entries on our open settlements list, such as the Visa and Mastercard ATM fee settlement, involve classes defined in the settlement agreement.

A denial is often the practical end of a consumer class case. The named plaintiffs can keep pursuing their own claims, but a few hundred dollars in individual damages rarely justifies years of litigation, so many cases settle individually or are dropped.

If you were only a member of a proposed class that was never certified, you generally keep your right to sue on your own. Under the Supreme Court's American Pipe rule, the filing of a class action pauses the statute of limitations for putative class members, and the clock generally starts again when certification is denied, so the time left to file your own case may be short. The American Pipe tolling rule dates to a 1974 Supreme Court decision and applies to members of the proposed class, not to people outside the class definition. Our guide on what happens if a class action loses explains more.

If a class that includes you is certified:

• You are in automatically. You do not need to sign anything to be included.
• You will get a chance to leave. For damages classes, the notice gives a deadline to opt out if you want to keep the right to sue on your own.
• You are represented by class counsel, who owe duties to the whole class. You can hire your own lawyer to appear in the case at your own expense.
• You will be bound by the outcome if you stay in, win or lose.

For a Rule 23(b)(3) damages class, the notice must state the time and manner for requesting exclusion and explain the binding effect of a class judgment. If your losses are much larger than the typical class member's, the opt-out decision deserves careful thought. A free case review takes about two minutes and connects you with independent attorneys who handle these cases. For background, see class action vs. individual lawsuit.