A procedure used in a lawsuit by which the court allows a third person who was not originally a party to the suit to become a party, by joining with either the plaintiff or the defendant.
The federal rules of CIVIL PROCEDURE recognizes two types of intervention: intervention of right and permissive intervention.
Intervention of right arises when the intervenor, the person who seeks to become a party to an existing lawsuit, can satisfactorily show that his or her interest is not adequately represented by the present parties, that the interest relates to the subject of the action, and that the disposition of the action might in some way impair his or her ability to protect such interest.
Permissive intervention is up to the discretion of the court. It arises when the intervenor's claim or defense and the instant suit have a QUESTION OF LAW or fact in common.
In deciding whether or not to permit intervention, the court ordinarily balances the needs and interest of the intervenor against the potential hardship on the existing parties if such intervention is allowed. The court will determine whether the intervenor and the parties to the suit share common issues. If the intervenor attempts to inject new causes of actions into the pending suit, his or her request will be denied, since to permit intervention would increase the potential for prejudice and delay in the original action. An intervenor need not argue that he or she will be prejudiced by the judgment if not joined, provided the intervenor is able to show that his or her interest will be impaired by the action if he or she is not involved.