Title IV: Parties · Last amended July 1, 2016 · Last verified July 14, 2026
In one sentenceRule 20 lets multiple plaintiffs or defendants join in a single lawsuit whenever their claims arise from the same transaction or occurrence and share a common question, while letting the court manage any unfairness that results.
(1)Plaintiffs. Persons may join in one action as plaintiffs if:
(A)they assert any right to relief jointly, severally, or in the alternative with respect to or arising out of the same transaction, occurrence, or series of transactions or occurrences; and
(B)any question of law or fact common to all plaintiffs will arise in the action.
(2)Defendants. Persons may be joined in one action as defendants if:
(A)any right to relief is asserted against them jointly, severally, or in the alternative with respect to or arising out of the same transaction, occurrence, or series of transactions or occurrences; and
(B)any question of law or fact common to all defendants will arise in the action.
(3)Extent of relief. Neither a plaintiff nor a defendant need be interested in obtaining or defending against all the relief demanded. The court may grant judgment to one or more plaintiffs according to their rights, and against one or more defendants according to their liabilities.
(b)Protective measures. The court may issue orders, including an order for separate trials, to protect a party against embarrassment, delay, expense, or other prejudice that arises from including a person against whom the party asserts no claim and who asserts no claim against the party. The court may also direct a final judgment on a claim of or against one or more parties as provided in Rule 54(b).
Amendment History
(Adopted March 1, 2016, effective July 1, 2016.)
Plain-English Summary
Rule 20 allows a lawsuit to grow beyond a single plaintiff and single defendant when doing so makes sense. Plaintiffs can join together if they're asserting rights arising out of the same transaction, occurrence, or series of events, whether jointly, severally, or in the alternative, and if some question of law or fact is common to all of them. The same logic applies to joining multiple defendants. Nobody needs to be interested in every bit of relief sought. The court can rule for some plaintiffs and against others, and hold some defendants liable while clearing others, all in the same case.
Bringing extra parties into a case can create its own headaches, so Rule 20 also gives the court tools to manage the mix. If including someone against whom a plaintiff makes no claim, or who makes no claim against the plaintiff, would cause embarrassment, delay, added expense, or other prejudice, the court can order separate trials or other protective measures. The court can also enter a final judgment on some claims while others continue, following the separate-judgment procedure in Rule 54(b).
Frequently Asked Questions
Can several people hurt in the same incident sue in one lawsuit?
Yes, if their claims arise from the same transaction, occurrence, or series of occurrences and share a common question of law or fact.
Do all plaintiffs need to seek the same relief to join together?
No. Rule 20 says no plaintiff needs to be interested in obtaining all the relief demanded in the case.
Can a court find some defendants liable but not others in a joined case?
Yes. The court may grant judgment for some plaintiffs and against some defendants according to their respective rights and liabilities.
What can I do if joining another party is unfairly prejudicial to me?
Ask the court for protective measures, including separate trials, under Rule 20(b).
How is Rule 20 different from Rule 18's joinder of claims?
Rule 18 governs how many claims one party can bring against another already in the case. Rule 20 governs whether additional parties can be joined in the first place.
Source & verification. Rule text
are reproduced verbatim from the Idaho Rules of Civil Procedure, adopted by the
Supreme Court of Idaho. Last verified July 14, 2026. ·
Official source
Also known as:joining multiple plaintiffspermissive joinder of partiesmultiple defendants one lawsuitsame transaction or occurrence claimsseparate trials for prejudice