Under which Rule is compulsory joinder established?

Compulsory joinder is established under Rule 19 of the Federal Rules of Civil Procedure. This rule addresses the necessity of joining parties that are essential to the resolution of the case. Specifically, Rule 19 outlines two categories of parties: necessary parties who must be joined if feasible and those who may be included because their absence would prevent a just adjudication of the action.

This rule serves to ensure that all parties whose interests might be affected by the court's decision are present in the litigation, which aids in preventing multiple lawsuits, inconsistent results, and incomplete relief. For example, if a plaintiff sues a defendant in an action that would also impact a third party's rights, Rule 19 mandates that the third party be joined in the lawsuit if it is feasible, ensuring comprehensive resolution of all claims.

The other rules mentioned serve different purposes: Rule 15 deals with amendments of pleadings, Rule 21 covers misjoinder and nonjoinder of parties, while Rule 14 pertains to third-party practice. Each of these rules addresses different aspects of party participation in litigation, but it is Rule 19 that specifically focuses on the concept of compulsory joinder.