Intervenor

An intervenor (or intervener in some jurisdictions) is a person or entity that participates in a legal proceeding after it has begun but was not an original party. The intervenor seeks to protect a legal or practical interest that could be affected by the outcome and might not be adequately represented by the existing parties.

In many common law systems, intervention can be as of right or discretionary (permissive). Intervention as of right is typically allowed when the applicant has a substantial, protected interest relating to the subject matter of the action, the interest may be impaired if not allowed to participate, the existing parties do not adequately represent the intervenor’s interest, and the intervention will not unduly delay or prejudice the proceedings. In the United States, these standards are reflected in rules governing intervention in civil actions. Permissive intervention is granted at the court’s discretion and usually requires a common question of law or fact and a consideration of potential prejudice and efficiency.

Rights and duties of an intervenor, once granted, can include filing pleadings, presenting evidence, participating in hearings, and cross-examining witnesses. The exact scope varies by jurisdiction and case type. Intervenors are generally bound by procedural orders and the court’s rulings, and their ability to appeal may hinge on their status as a party to the action.

Intervenors are common in civil litigation, regulatory and administrative proceedings, and environmental or public-interest cases, where broader input helps ensure that affected interests are considered. The terminology and precise rules vary by jurisdiction, with “intervenor” being standard in many Commonwealth countries.