Federal Rule of Civil Procedure 21, which governs misjoinder and nonjoinder of parties, tells federal courts that having the wrong parties in a lawsuit, or missing a party who should be there, is not by itself a reason to dismiss the case. Instead, the court can add or drop a party at any time on just terms, and it can sever any claim against a party into its own separate action.
The Text of Rule 21
The rule is three sentences long: “Misjoinder of parties is not a ground for dismissing an action. On motion or on its own, the court may at any time, on just terms, add or drop a party. The court may also sever any claim against a party.”1Legal Information Institute. Federal Rules of Civil Procedure Rule 21 – Misjoinder and Nonjoinder of Parties Those three sentences give courts broad discretion to reshape a case from filing through judgment, and they work alongside several other rules that define who belongs in a lawsuit and how parties can be added.
What Misjoinder Means
Misjoinder happens when someone has been included in a lawsuit who does not belong there. The test comes from Rule 20, which requires that jointly named parties share claims arising out of the same transaction or series of events and that there be at least one common question of law or fact linking them.2Legal Information Institute. Federal Rules of Civil Procedure Rule 20 – Permissive Joinder of Parties If a party fails either prong, they are misjoined.
A common example: a plaintiff sues two defendants over two unrelated contract disputes just to save the trouble of filing separately. The claims do not share a common transaction and do not raise overlapping factual questions, so bundling those defendants into one case is improper. The same problem arises when two plaintiffs injured in separate incidents on different dates try to sue the same defendant together without any shared factual or legal thread.
Under Rule 21, that mistake does not sink the case. The court drops the misjoined party or severs their claims into a separate action, and the rest of the lawsuit continues.1Legal Information Institute. Federal Rules of Civil Procedure Rule 21 – Misjoinder and Nonjoinder of Parties
What Nonjoinder Means
Nonjoinder is the opposite: someone who should be in the lawsuit has been left out. Rule 19 defines who counts as a “required” party. A person is required if the court cannot give complete relief to the existing parties without them, if their absence would impair their own ability to protect a legal interest, or if their absence would leave existing parties exposed to conflicting obligations from separate lawsuits.3Legal Information Institute. Federal Rules of Civil Procedure Rule 19 – Required Joinder of Parties
Consider a dispute over ownership of real estate where three people each claim an interest but only two are named. The court cannot fully resolve who owns what without the third claimant. Contract cases raise a similar issue when all signatories need to be at the table for the court to interpret everyone’s rights.
When Nonjoinder Can Still Lead to Dismissal
Rule 21’s promise not to dismiss for party problems has a real limit. If a required party cannot be joined, because they are outside the court’s jurisdiction or because adding them would destroy diversity jurisdiction, Rule 19(b) requires the court to decide whether to proceed without them or dismiss the case.3Legal Information Institute. Federal Rules of Civil Procedure Rule 19 – Required Joinder of Parties Four factors guide that decision:
- How much prejudice a judgment would cause to the absent party or to the existing parties.
- Whether protective measures, such as a narrower remedy or conditions on the judgment, could reduce that prejudice.
- Whether a judgment rendered in the party’s absence would be adequate.
- Whether the plaintiff would have an adequate remedy if the action were dismissed for nonjoinder.
A party who cannot be joined and whose absence makes fair resolution impossible is sometimes called “indispensable.” When that label applies, dismissal is a real possibility. It comes from Rule 19(b), not from Rule 21.
How Parties Get Added or Dropped
Any party can file a motion to add or drop someone, and the court can act on its own without a motion.1Legal Information Institute. Federal Rules of Civil Procedure Rule 21 – Misjoinder and Nonjoinder of Parties The change can happen at any stage: early in the case, during discovery, at trial, or even after judgment. A motion should explain the reason. To argue misjoinder, show that the claims against the party do not arise from the same transaction as the rest of the case or that no common question of law or fact ties them in. To argue nonjoinder, show why the missing person is required under Rule 19.
The phrase “on just terms” gives the court flexibility to attach conditions. A court might grant a newly added party extra time to prepare a defense, shift certain costs, or adjust discovery deadlines so no one is blindsided by a mid-case change to the lineup.
Rule 21 and Rule 15: Amending the Complaint
Adding a party usually also requires amending the complaint, which brings Rule 15 into play. Rule 15 directs courts to “freely give leave when justice so requires.”4Legal Information Institute. Federal Rules of Civil Procedure Rule 15 – Amended and Supplemental Pleadings In practice, a plaintiff who wants to add a new defendant often needs to satisfy both rules: Rule 21 for authority to change the party lineup, and Rule 15 for permission to file the amended pleading that names the new party.
Timing matters. Under Rule 15(c), an amendment adding a new party can “relate back” to the original filing date, preserving the claim even if the statute of limitations has since expired, but only if the new party received notice of the lawsuit within the time allowed for service and knew or should have known they would have been named originally but for a mistake about their identity.4Legal Information Institute. Federal Rules of Civil Procedure Rule 15 – Amended and Supplemental Pleadings That window is narrow, and missing it can be fatal to a claim against a late-added party.
Severance Under Rule 21
Beyond adding and dropping parties, Rule 21 lets the court sever claims. Severance splits part of a case into an entirely separate lawsuit with its own docket number, its own timeline, and potentially its own trial.1Legal Information Institute. Federal Rules of Civil Procedure Rule 21 – Misjoinder and Nonjoinder of Parties It is most useful when a misjoined party’s claims do not warrant outright dismissal but should not stay in the same action.
Severance under Rule 21 is not the same as a separate trial under Rule 42(b). With Rule 42, the claims stay in the same case and are simply tried at different times for convenience, to avoid prejudice, or to save time and money.5Legal Information Institute. Federal Rules of Civil Procedure Rule 42 – Consolidation; Separate Trials With Rule 21 severance, the severed claims become a completely independent action. That distinction matters for appeals, for case management going forward, and for jurisdiction.
Statute of Limitations Concerns
Severance and the statute of limitations interact in a way that can catch parties off guard. When a party is dropped from a case for misjoinder, the time their claims were pending in the original lawsuit generally does not toll the limitations period. If the deadline expired while those claims sat in the wrong case, the dropped party may find they can no longer refile. Severance avoids that trap: sending claims to a new docket rather than dismissing them preserves the original filing date. This is one reason severance is often the better remedy when a limitations problem lurks in the background.
Using Rule 21 to Fix Jurisdictional Problems
One of Rule 21’s most practical uses has little to do with misjoinder in the traditional sense. Federal courts regularly use it to drop a dispensable nondiverse party whose presence destroys diversity jurisdiction. If a plaintiff sues three defendants in federal court based on diversity but one defendant shares a state of citizenship with the plaintiff, the court can drop that defendant under Rule 21 to preserve jurisdiction over the remaining claims, provided the dropped defendant is not required under Rule 19. The Supreme Court has confirmed that Rule 21 authorizes dropping a dispensable nondiverse party at any time, including after judgment.
This jurisdictional use shows up often in removal cases. When a defendant removes a case to federal court and the plaintiff argues that a nondiverse co-defendant destroys jurisdiction, the removing defendant may invoke Rule 21 to sever or drop the jurisdiction-spoiling party. The court then evaluates whether that party is truly dispensable under Rule 19 before deciding whether to keep the case.