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Intervention is a procedural method for a third-party to enter an already existing action. In federal courts, intervention is regulated by Federal Rule of Civil Procedure (FRCP) 24

FRCP 24(a) allows intervention of right, where a court must permit intervention upon timely motion by (1) any third-party that has an unconditional right to intervene under federal statute or (2) any third-party that claims an interest relating to the property or transaction that is the subject of the action and where disposing of the action would practically impair or impede the third-party’s ability to protect their interest, unless existing parties adequately represent the interest. The purpose of intervention of right is to allow third-parties with interests at stake to enter the action without waiting to be brought in by parties to the lawsuit and to avoid affecting the interests of non-parties without their representation in the action.

FRCP 24(b) allows permissive intervention upon timely motion by any third-party that (1) has a conditional right to intervene under federal statute or (2) has a claim or defense that shares a common question of law or fact with the main action. Permissive intervention is also allowed for government officers or agencies if a party’s claim or defense is based on a statute or executive order administered by the officer or agency or any regulation, order, requirement, or agreement issued or made under the statute or executive order. For permissive intervention, courts have discretion to consider whether the intervention will unduly delay or prejudice the adjudication of the original parties’ rights. 

A motion to intervene requires service on the parties to the suit, a statement of the grounds for intervention, and a pleading that includes the claims or defenses for which the intervention is sought.

[Last updated in June of 2023 by the Wex Definitions Team]