Joinder of a party that is not permitted under Rule 20(a) is not a ground to dismiss an entire action. At any time—on terms that are just—the court may dismiss an improperly joined party or join any party who may be properly joined under Rule 20(a). The court may also sever any claim against a party, and that severed claim may proceed as a separate and independent action.
Rule 21.Improper joinder and nonjoinder of parties; severance.
Last verified July 1, 2026
In one sentenceRule 21 makes clear that joining a party improperly is never grounds to dismiss an entire case, and instead lets the court, at any time and on just terms, drop a misjoined party, add a party who should be joined, or sever any claim into its own separate action.
Full Text of Rule 21
Amendment History
Promulgated by R-16-0010, effective January 1, 2017.
Plain-English Summary
Rule 21 protects a case from being thrown out just because someone was added who should not have been, or because Rule 20’s joinder requirements were not perfectly met. Instead of dismissal, the court can act at any point in the case — on terms that are fair to everyone — to drop the improperly joined party, add a party who belongs in the case under Rule 20, or split off any claim into its own independent lawsuit.
That flexibility lets a court fix a joinder mistake without penalizing the rest of the case, and it gives the court a tool to manage a lawsuit that has grown unwieldy by carving out a particular claim to proceed on its own track.
Frequently Asked Questions
Can a whole lawsuit be dismissed because a party was improperly joined?
No, misjoinder is never grounds to dismiss the entire action.
What can a court do instead of dismissing a case over a joinder problem?
Drop the improperly joined party, add a party who should be joined, or sever a claim into its own separate action.
Is there a deadline for fixing a joinder problem under Rule 21?
No, the court may act at any time, on terms that are just.
Source & verification. The rule text and History are reproduced verbatim from the
official Arizona Rules of Civil Procedure (Ariz. R. Civ. P. 21). Prescribed by the Supreme Court of Arizona (Ariz. Const. art. 6, § 5). The plain-English summary is original and written by us. Last verified July 1, 2026. ·
Official source
Also known as: improper joindermisjoinderseverance of claims