To start a class action lawsuit, you file a standard civil complaint in federal court on behalf of yourself and a defined group of people harmed the same way, plead the four requirements of Rule 23 of the Federal Rules of Civil Procedure, serve the defendant, and then move the court to certify the case as a class action. Filing the complaint is the easy part. The case does not actually become a class action until a judge grants certification, and that fight can take months or years of litigation to resolve.
The steps below track what you and your attorney will need to do, in the order you will need to do them.
Build the Case Before You File
The work that determines whether a class action survives starts before anything is filed. You need documentation that shows the specific harm and ties it to the defendant’s conduct: purchase receipts, contracts, billing statements, medical records, correspondence, or screenshots of misleading marketing. A clear timeline of what happened and when gives the eventual complaint a spine.
You also need the right lead plaintiff, and that choice is one of the most consequential decisions in the case. The representative’s claims should be typical of the group’s, with no unusual defenses the defendant can exploit and no conflicts with other members. Courts scrutinize a lead plaintiff’s credibility and motivation. A buyer with a single clean transaction and a preserved receipt is a stronger representative than someone with a tangled history and a separate personal grievance against the company.
Serving as a lead plaintiff is real work. Expect depositions, document review, and years of availability. Courts sometimes approve a modest incentive payment at the end of the case for that effort, but the amount requires court approval and judges reject figures they consider excessive relative to what the class recovered.
File the Complaint
A class action complaint reads like a standard federal civil complaint with additional allegations bolted on. Beyond the facts and legal claims, it must propose a class definition, name the lead plaintiff as class representative, allege that the case satisfies Rule 23’s prerequisites, identify which Rule 23(b) category the case falls under, and explain why a class action is the right vehicle.
Two administrative forms go with the complaint. The Civil Cover Sheet (Form JS 44) requires your attorney to categorize the lawsuit by jurisdictional basis and nature of suit, and to check the box marking the case as a Rule 23 class action. The Summons in a Civil Action (Form AO 440) is the document that formally notifies the defendant and states the deadline for a response.
Filing with the clerk of the district court triggers a fee of $405, which is the $350 statutory fee under 28 U.S.C. ยง 1914 plus a $55 administrative fee set by the Judicial Conference of the United States.1Office of the Law Revision Counsel. 28 USC Ch 123 – Fees and Costs Most federal courts require electronic filing through the CM/ECF system. If a corporate party is involved, Rule 7.1 requires a disclosure statement identifying any parent corporation and any publicly held company that owns 10 percent or more of its stock.2Legal Information Institute (LII) at Cornell Law School. Federal Rules of Civil Procedure Rule 7.1 – Disclosure Statement
Serve the Defendant Within 90 Days
After filing, you must serve the defendant with the complaint and summons, either through a professional process server or a U.S. Marshal. Service has to be completed within 90 days of filing. Miss that window and the court can dismiss the case without prejudice, which means starting over.3Legal Information Institute. Federal Rules of Civil Procedure Rule 4 – Summons Botched service is one of the most avoidable ways to lose months of work, so get it right the first time.
Confirm the Case Belongs in Federal Court
Most large class actions proceed in federal court because of the Class Action Fairness Act, enacted in 2005. CAFA gives federal district courts jurisdiction over class actions when three conditions are met: the combined claims of all class members exceed $5 million, the proposed class has at least 100 members, and at least one class member is a citizen of a different state than at least one defendant. That last requirement, called minimal diversity, is far easier to satisfy than the complete diversity ordinarily required in federal court.
CAFA also lets defendants remove a class action originally filed in state court to federal court when those thresholds are met. There are carve-outs. A federal court must decline jurisdiction when more than two-thirds of the class members and the primary defendants are citizens of the state where the case was filed, and it has discretion to decline when between one-third and two-thirds of the class shares citizenship with the primary defendants in the filing state.
The Four Requirements Your Case Must Satisfy
Every class action lives or dies on Rule 23(a). Courts apply the four tests strictly, and failing any one of them ends class treatment.
Numerosity. The proposed group has to be large enough that joining every member individually would be impractical. The rule sets no magic number, but courts routinely find this satisfied above roughly 40 members. A recall affecting thousands of buyers or a breach exposing millions of accounts clears the bar easily. Fifteen people probably does not.
Commonality. There must be at least one question of law or fact shared across the whole group, and the answer to that question must actually resolve an issue central to every member’s claim in one stroke. A uniform corporate policy that shorted overtime to all hourly workers creates strong commonality. A situation where each member’s injury turns on unique individual facts does not.
Typicality. The lead plaintiff’s claims have to mirror the class’s. The experience does not need to be identical to every member’s, but the core legal and factual basis has to overlap. A representative with a substantially different injury, or one facing a defense that does not apply to others, will drag the trial into issues the class does not share.
Adequacy. The court looks at both the lead plaintiff and the attorneys. The representative must have no conflicts with the rest of the class and enough personal stake to stay engaged for years. Counsel must show the resources, experience, and competence to run complex group litigation. This is the court’s safeguard against settlements that reward the lead plaintiff and shortchange everyone else.
Which Rule 23(b) Category the Case Fits
Meeting the four prerequisites is only half of it. The case also has to fit one of three categories under Rule 23(b), and the category matters because it controls whether members can leave the lawsuit.
- Rule 23(b)(1) covers situations where separate individual lawsuits could produce conflicting judgments that would force the defendant into contradictory obligations. Members cannot opt out.
- Rule 23(b)(2) covers cases seeking injunctive or declaratory relief, where the defendant acted or refused to act in a way that affects the entire class uniformly. Civil rights cases often proceed here. Members cannot opt out.
- Rule 23(b)(3) is the workhorse for damages cases. The court has to find that common questions predominate over individual ones and that a class action is superior to individual lawsuits. This is the only category where members have the right to opt out and pursue their own claims.
Most consumer fraud, defective product, and securities class actions proceed under Rule 23(b)(3), which triggers notice and opt-out requirements after certification.
Move for Class Certification
A case does not become a class action at filing. That transformation requires a separate motion for class certification, usually filed after an initial round of discovery focused on class-related issues. The plaintiff’s brief has to lay out detailed evidence that each Rule 23(a) prerequisite is met and that the case fits a Rule 23(b) category. The defendant will oppose, typically arguing that individual issues dominate or that the proposed class definition is too broad.
The judge may hold a hearing. If the court grants the motion, it issues a Certification Order that defines the class, identifies the claims, and appoints class counsel under Rule 23(g).4Legal Information Institute (LII) / Cornell Law School. Federal Rules of Civil Procedure Rule 23 – Class Actions For a Rule 23(b)(3) class, the court also approves a plan for notifying all identifiable members. That notice must explain the claims, the class definition, and the right to opt out, along with a deadline. Courts prefer that members get at least 60 to 90 days to decide.
Class counsel appointed under Rule 23(g) owes a duty to the entire class, not just to the lead plaintiff. That distinction matters when settlement talks begin, because counsel has to weigh what is fair for every member rather than optimize for any one person.
If Certification Is Denied
A denial does not automatically end the case. Either side can petition the court of appeals for permission to take an immediate interlocutory appeal under Rule 23(f), but the petition has to be filed within 14 days of the certification order. The appeals court has full discretion to accept or reject it, and filing the petition does not pause the district court proceedings unless a judge specifically orders a stay.
If certification fails and no appeal succeeds, the lead plaintiff’s individual claims can still go forward as a regular lawsuit. Under the tolling doctrine from American Pipe & Construction Co. v. Utah, the statute of limitations for every putative class member is paused from the moment the class complaint was filed until the certification decision. That gives other people time to file their own individual suits even if the class vehicle collapses.
How Your Attorney Gets Paid
Lead plaintiffs almost never pay class counsel out of pocket. Class action lawyers work on contingency, collecting fees only if the case produces a recovery. Courts use two methods to size the fee.
The percentage-of-recovery method awards attorneys a share of the total amount recovered for the class, typically 25 to 33 percent, with the court free to go higher or lower based on complexity and risk.
The lodestar method multiplies hours reasonably spent by a reasonable hourly rate, then may apply a multiplier up or down. Multipliers of two or three are not unusual in high-risk cases with exceptional results. This method shows up more often when a statute authorizes attorney fees rather than when fees come out of a common fund.
In common fund cases, courts tend to favor the percentage approach. Either way, the fee needs judicial approval, and class members can object if they consider the request excessive.
Watch the Filing Deadline
Every claim has a statute of limitations, and it drives everything in the early stages. Under American Pipe, filing a class action pauses that clock for every person who falls within the proposed class definition, from the date the complaint is filed until the court rules on certification. If certification is granted, members who stay in are covered by the class case. If it is denied, tolling stops and the clock starts running again immediately, which is when individual plaintiffs need to move quickly on their own suits.