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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.


n. the procedure under which a third party may join an on-going law-suit, providing the facts and the law issues apply to the intervenor as much as to one of the existing contestants. The determination to allow intervention is made by a judge after a petition to intervene and a hearing on the issue. Intervention must take place fairly early in the lawsuit, shortly after a complaint and answer have been filed, and not just before trial since that could prejudice one or both parties who have prepared for trial on the basis of the original litigants. Intervention is not to be confused with joinder which involves requiring all parties who have similar claims to join in the same lawsuit to prevent needless repetitious trials based on the same facts and legal questions, called multiplicity of actions. (See: intervene, joinder)


(Imposition into a lawsuit), noun ennrance into a lawsuit, entrance of a third party, insertion, interference, interjection, interjection into a lawsuit, intrusion
Associated concepts: intervention by leave of the court, innervention by right


(Interference), noun intercalation, intercession, interjacence, interjection, interloping, intermeddling, intermediation, interpolation, interposition, interruption, interventus, intrusion
See also: agency, arbitration, collective bargaining, intercession, invasion, mediation

INTERVENTION, civil law. The act by which a third party becomes a party in a suit pending between other persons.
     2. The intervention is made either to be joined to the plaintiff, and to claim the same thing he does, or some other thing connected with it or, to join the defendant, and with him to oppose the claim of the plaintiff, which it is his interest to defeat. Poth. Proced. Civ. lere part. ch. 2, s. 6, Sec. 3. In the English ecclesiastical courts, the same term is used in the same sense.
     3. When a third person, not originally a party to the suit or proceeding, but claiming an interest in the subject-matter in dispute, may, in order the better to protect such interest, interpose his claim, which proceeding is termed intervention. 2 Chit. Pr. 492; 3 Chit. Com. Law, 633; 2 Hagg. Cons. R. 137; 3 Phillim. R. 586; 1 Addams, R. 5; Ought. tit. 14; 4 Hagg. Eccl. R. 67 Dual. Ad. Pr. 74. The intervener may come in at any stage of the cause, and even after judgment, if an appeal can be allowed on such judgment. 2 Hagg. Cons. R. 137: 1 Eng. feel. R. 480; 2 E.g. Eccl. R. 13.

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Thus, consistent with assumptions found in the metatheory of multicultural counseling and therapy (Sue, Ivey, & Pedersen, 1996), career intervention models for working with racial and ethnic minorities support the premise that counseling is more effective if the career counselor incorporates the life experiences, worldview, and multiple identities of the client into problem conceptualization and intervention planning.
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We identified 66 intervention studies to improve prescribing of antimicrobial drugs to hospital inpatients that met our inclusion criteria (16) and excluded 243 studies that were uncontrolled before and after studies (n = 164) or inadequate ITS studies (n = 79).
Preventive Services Task Force (USPSTF) reviewed 12 controlled studies of problem drinkers in primary care settings, including very brief intervention (5 minutes or less, one time) and brief interventions (5-15 minutes, one time): Three of seven studies showed reduced alcohol use among patients who received the intervention.
The formal intervention that resulted in my successful recovery from alcoholism took place on June 8, 1982.
Strategies of crisis intervention are based on psychological theory, yet are adapted and modified to fit the demands of the crisis situation (James & Gilliland, 2001).
Early Intervention Programs provide support, information as well as educate parents in order to maximize their child's development.
The names of all freshmen were concealed throughout the project until the intervention phase, which Thompson developed with the Department of Academic Affairs.