Rule 24.Intervention

Rule 24(a) sets out intervention of right: on a timely motion, the court must let someone into a pending case if a statute gives that person an unconditional right to intervene, or if the person claims an interest in the property or transaction at issue and the case's disposition could, as a practical matter, impair or impede that interest — unless the parties already in the case adequately represent it. Because intervention of right is mandatory once those conditions are met, timeliness matters; a motion filed too late in the case can defeat an otherwise valid claim to intervene.

Rule 24(b) covers permissive intervention, which rests in the court's discretion rather than being mandatory. The court may allow someone to intervene if a statute gives a conditional right to do so, or if the person's claim or defense shares a common question of law or fact with the pending action. A federal or state government officer or agency may also seek permissive intervention when a party's claim or defense rests on a statute or executive order the agency administers, or on a regulation, order, requirement, or agreement issued under it. Whatever the basis, the rule directs the court to weigh whether letting the newcomer in will unduly delay or prejudice the existing parties' rights.

Rule 24(c) sets the mechanics: a motion to intervene must be served on the parties under Rule 5, state the grounds for intervention, and come with a pleading laying out the claim or defense the intervenor wants to raise — the same procedure applies even when a statute itself confers the right to intervene. Rule 24(c)(2) adds a distinct safeguard for constitutional challenges: if a party questions the constitutionality of a legislative act affecting the public interest, and neither the state nor any state agency or officer is already a party, that party must notify the attorney general, who the court must then permit to intervene on a timely motion on the state's behalf.