Fed. R. Civ. P. 24 — Intervention
Last verified: May 19, 2026 · U.S. Courts — FRCP.
Rule Text — Key Provisions
(a) Intervention of right. Court must permit anyone to intervene who: (1) is given an unconditional right by federal statute; or (2) claims an interest relating to the subject of the action, and disposing of the action may impair their ability to protect that interest, unless existing parties adequately represent it.
(b) Permissive intervention. On timely motion, court may permit intervention by anyone who: (1) has a conditional statutory right; or (2) has a claim or defense sharing a common question of law or fact with the main action.
(c) Notice and pleading required. Motion to intervene must be served on parties and state the grounds, accompanied by a pleading setting out the claim or defense.
Full text: law.cornell.edu/rules/frcp/rule_24.
Plain English
Rule 24 lets a non-party join an existing case. Two flavors: intervention of right (you have a legal interest the case will affect) and permissive intervention (your claim shares facts or law with the existing case). The former is mandatory if you meet the test; the latter is discretionary.
Key Cases & Authority
- NAACP v. New York, 413 U.S. 345 (1973) — Timeliness factors for intervention motions: stage of proceedings, prejudice to existing parties, prejudice to intervenor if denied, unusual circumstances.
- Trbovich v. United Mine Workers, 404 U.S. 528 (1972) — Established the “minimal” adequacy-of-representation standard: prospective intervenor must only show representation “may be” inadequate.
- Cascade Natural Gas Corp. v. El Paso Natural Gas Co., 386 U.S. 129 (1967) — Antitrust intervention case still cited on what constitutes a sufficient interest.
- Berger v. North Carolina State Conference of NAACP, 597 U.S. 179 (2022) — State legislative leaders had a right to intervene in litigation challenging state law where state officials disagreed about defense.
Florida Parallel
Fla. R. Civ. P. 1.230 — Florida’s intervention rule is simpler and entirely discretionary. There is no “intervention of right” under Florida state-court practice the way Rule 24(a) creates in federal court.
About this rule walkthrough
Part of The Federal Rule Book, hosted by John M. Phillips — Board Certified Civil Trial Lawyer, Court TV analyst, admitted in 8 states + 9 federal districts + SCOTUS.
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Educational only — not legal advice.
Rule Text (verbatim from the Florida Supreme Court)
(a) Intervention of right. On timely motion, the court must permit anyone to intervene who: (1) is given an unconditional right to intervene by a federal statute; or (2) claims an interest relating to the subject of the action, and is so situated that disposing of the action may impair the movant’s ability to protect that interest, unless existing parties adequately represent it.
(b) Permissive intervention. On timely motion, the court may permit anyone to intervene who: (1) has a conditional right by federal statute; or (2) has a claim or defense that shares with the main action a common question of law or fact.
(c) Motion to intervene must be served on parties, state grounds, and be accompanied by a pleading setting out the claim or defense.
Educational reference. This page summarizes a Federal Rule of Civil Procedure for educational purposes. It is not legal advice. Federal procedural rules can change — always verify the current text at uscourts.gov before relying on this summary in any case.
What this rule means in plain English
Rule 24 lets a non-party join an existing federal case. Two flavors: intervention of right (you have a legal interest the case will affect) and permissive intervention (your claim shares facts or law with the existing case). The former is mandatory if you meet the test; the latter is discretionary. Timeliness is usually decisive.