Joinder of parties is a procedural device used by courts and tribunals to combine multiple claimants or respondents into a single proceeding, either because their participation is necessary for a just resolution or because doing so promotes efficiency and avoids inconsistent rulings. In domestic litigation, joinder rules typically distinguish between compulsory (or "necessary") joinder, where a party must be added because the case cannot be fully resolved without them, and permissive joinder, where a party may be added if their claim shares a common question of law or fact with the existing dispute.
In the United States, joinder is governed primarily by Rules 19 and 20 of the Federal Rules of Civil Procedure. Rule 19 covers required parties whose absence would prejudice existing parties or prevent complete relief; Rule 20 governs permissive joinder where claims arise out of the same transaction or occurrence. Comparable mechanisms exist in the English Civil Procedure Rules (Part 19) and in most civil-law jurisdictions under doctrines of litisconsorcio or Streitgenossenschaft.
In international law, joinder appears in several forms. The International Court of Justice may join proceedings under Article 47 of its Rules of Court, as it did in the South West Africa cases (Ethiopia and Liberia v. South Africa) in 1961. Investor-state arbitration tribunals occasionally permit joinder where consent and procedural rules allow, though the absence of a treaty-based right of non-disputing parties to join remains contested. The International Criminal Court permits victim participation under Article 68(3) of the Rome Statute, a related but distinct concept.
Key functions of joinder include:
- Judicial economy: avoiding duplicative litigation
- Consistency: preventing contradictory judgments on the same facts
- Completeness of relief: ensuring all interested parties are bound
- Due process protection: safeguarding absent parties whose interests are at stake
Joinder is generally distinguished from intervention, which is initiated by the third party rather than by the existing litigants or the court.
Example
In 1961, the ICJ joined the proceedings brought separately by Ethiopia and Liberia against South Africa concerning the mandate over South West Africa, treating them as a single case.
Frequently asked questions
Joinder is initiated by the existing parties or ordered by the court to add another party; intervention is initiated by a third party seeking to enter ongoing litigation on its own motion.
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