In one sentenceRule 24 lets a court permit someone outside a lawsuit to join it, either as of right when the person’s interest could be impaired without joining and no one already in the case adequately represents that interest, or permissively when the person shares a common question of law or fact with the case, and it sets the timing and paperwork a would-be intervenor must follow.
aIntervention of right. On timely motion, the court must permit anyone to intervene who:
1has an unconditional right to intervene under a statute; or
2claims an interest relating to the subject of the action, and is so situated that disposing of the action in the person’s absence may as a practical matter impair or impede the person’s ability to protect that interest, unless existing parties adequately represent that interest.
1Generally. On timely motion, the court may permit anyone to intervene who:
Ahas a conditional right to intervene under a statute; or
Bhas a claim or defense that shares with the main action a common question of law or fact.
2By a government officer or agency. On timely motion, the court may permit a state governmental officer or agency to intervene if a party’s claim or defense is based on:
Aa statute administered by the officer or agency; or
Bany regulation, order, requirement, or agreement issued or made under a statute administered by the officer or agency.
3Delay or prejudice. In exercising its discretion over permissive intervention, the court must consider whether the intervention will unduly delay or prejudice the adjudication of the original parties’ rights.
1Requirements of motion. Anyone moving to intervene must:
Aserve the motion on the parties as provided in Rule 5(c); and
Battach as an exhibit to the motion a copy of the proposed pleading in intervention that sets out the claim or defense for which intervention is sought.
2Filing and serving pleading in intervention. Unless the court orders otherwise, an intervenor must file and serve the pleading in intervention within 10 days after entry of the order granting the motion to intervene.
3Response to pleading in intervention. If the pleading in intervention is one to which a party must respond, that party must plead in response to the pleading in intervention within 20 days after it is served. If the pleading in intervention does not require a party to file a responsive pleading, that party may plead in response to the pleading in intervention within 20 days after it is served.
Amendment History
Promulgated by R-16-0010, effective January 1, 2017.
Plain-English Summary
Rule 24 lets someone who is not already a party ask to join a pending lawsuit. Subdivision (a) covers intervention of right: on a timely motion, the court must let the applicant in if a statute grants an unconditional right to intervene, or if the applicant claims an interest in the subject of the action that could, as a practical matter, be impaired or impeded by the case going forward without them, unless the parties already in the case adequately represent that interest.
Subdivision (b) covers permissive intervention, which rests in the court's discretion rather than being guaranteed. A court may allow someone to intervene if a statute gives a conditional right to do so, or if the applicant's claim or defense shares a common question of law or fact with the main action; a state officer or agency can seek the same kind of permissive intervention when a party's claim or defense rests on a statute or regulation that officer or agency administers. Either way, the underlying motion must be timely, and for permissive intervention the rule also directs the court to consider whether allowing the intervention will unduly delay or prejudice the rights of the parties already in the case.
Subdivision (c) sets the mechanics: anyone moving to intervene must serve the motion on the existing parties and attach a proposed pleading spelling out the claim or defense the intervention seeks to advance. Once the court grants the motion, the intervenor must file and serve that pleading within 10 days unless the court sets a different deadline, and any party who must respond to it has 20 days to do so.
Frequently Asked Questions
What’s the difference between intervention of right and permissive intervention?
Intervention of right (subdivision (a)) is something the court must allow when a statute grants that right, or when the applicant’s interest could be impaired and isn’t already adequately represented. Permissive intervention (subdivision (b)) rests in the court’s discretion, typically when the applicant shares a common question of law or fact with the case.
Does a court have discretion to deny intervention of right when the conditions are met?
No, the court must permit intervention of right once its conditions are satisfied, unlike permissive intervention, which the court may grant or deny.
What must someone do to formally move to intervene?
Serve the motion on the existing parties and attach a proposed pleading setting out the claim or defense the intervention would raise.
How much time does an intervenor have to file its pleading once the motion to intervene is granted?
10 days after the order granting the motion, unless the court sets a different deadline.
Source & verification. The rule text and History are reproduced verbatim from the
official Arizona Rules of Civil Procedure (Ariz. R. Civ. P. 24). 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:interventionintervention of rightpermissive interventionmotion to intervene