Misjoinder

In legal practice, misjoinder occurs when a party or claim is improperly combined with others in a single proceeding, violating the procedural rules that govern who or what may be litigated together. Rules of civil procedure typically allow joinder only when claims arise from the same transaction or occurrence, or share a common question of law or fact. When that nexus is missing, the joinder is improper.

There are two main forms:

• Misjoinder of parties — adding a plaintiff or defendant who has no proper connection to the dispute (for example, suing two unrelated defendants in one action over separate incidents).
• Misjoinder of claims — combining causes of action that do not meet the procedural threshold for being heard together.

In the United States, Federal Rule of Civil Procedure 21 addresses the remedy: misjoinder is not a ground for dismissing the action. Instead, the court may, on motion or on its own, add or drop a party, or sever any claim against a party. Similar principles appear in the Civil Procedure Rules of England and Wales (CPR Part 19) and in most common-law jurisdictions.

In criminal procedure, misjoinder takes on heightened significance because trying defendants or charges together can prejudice the accused. Under U.S. Federal Rule of Criminal Procedure 8, offenses or defendants may be joined only if they are of the same or similar character, or are based on the same act or transaction. Rule 14 permits severance where joinder causes prejudice. The U.S. Supreme Court addressed related concerns in Zafiro v. United States (1993), holding that severance is required only when there is a serious risk that a joint trial would compromise a specific trial right.

For researchers and MUN delegates studying international tribunals, analogous issues arise in the joinder and severance decisions of the ICTY, ICTR, and ICC, where chambers weigh judicial economy against fair-trial rights of co-accused.