Rule 19.Joinder of persons needed for just adjudication

Rule 19(a) identifies who must be joined, if joinder is feasible, without depriving the court of subject-matter jurisdiction: a person whose absence would leave complete relief impossible among the parties already in the case, or a person who claims an interest in the subject of the action and whose absence might impair that person's ability to protect the interest, or leave existing parties exposed to double, multiple, or otherwise inconsistent obligations because of the claimed interest. If such a person hasn't been joined, the court orders that they be made a party. Someone who should join as a plaintiff but refuses can instead be made a defendant, or, in a proper case, an involuntary plaintiff. And if that person objects to venue and joining them would render the action's venue improper, the rule requires dismissing that person from the action rather than proceeding with improper venue.

Rule 19(b) addresses the harder case: what happens when that person can't be joined at all. The court then decides, in equity and good conscience, whether the action should proceed among the parties already before it or should be dismissed, treating the absent person as indispensable. Four factors guide that call: how much a judgment rendered in the person's absence might prejudice the person or the existing parties; whether protective provisions in the judgment, shaping the relief, or other measures could lessen or avoid that prejudice; whether a judgment rendered without the absent person would be adequate; and whether the plaintiff would have an adequate remedy if the action were dismissed for nonjoinder.

Rule 19(c) adds a disclosure duty. A pleading asserting a claim for relief must name any person described in Rule 19(a)(1)-(2) who wasn't joined, if the pleader knows the name, and state the reasons for leaving that person out.