Rule 24.Intervention

Rule 24(a) covers intervention of right. On timely application, anyone must be permitted to intervene when a statute confers an unconditional right to do so, or when the applicant claims an interest in the property or transaction that is the subject of the action, and disposing of the action without the applicant may as a practical matter impair or impede the applicant's ability to protect that interest — unless an existing party already adequately represents that interest.

Rule 24(b) covers permissive intervention, which rests in the court's discretion. On timely application, someone may intervene when a statute confers a conditional right to do so, or when the applicant's claim or defense shares a question of law or fact with the main action. The rule also lets a state officer or agency intervene, on timely application, when a party relies on a statute, executive order, regulation, order, requirement, or agreement that officer or agency administers or issued. In deciding whether to allow permissive intervention, the court must consider whether it will unduly delay or prejudice the adjudication of the existing parties' rights.

Rule 24(c) sets the procedure: whoever wants to intervene serves a motion on the parties under Rule 5, states the grounds for intervention in the motion, and attaches a pleading setting out the claim or defense for which intervention is sought. The same procedure applies when a statute gives the right to intervene.