Rule 19.Required Joinder of Parties

Rule 19(a) identifies who must be joined to a lawsuit if it is possible to do so. A person who can be served with process and whose joinder would not destroy the court's subject matter jurisdiction must be added if the court cannot grant complete relief among the parties already in the case without them, or if that person claims an interest in the subject of the suit and proceeding without them could, as a practical matter, hurt their ability to protect that interest or leave an existing party exposed to double, multiple, or inconsistent obligations because of it.

If a required person has not been joined, the court must order it done on its own. Someone who refuses to join voluntarily as a plaintiff can be made a defendant instead, or, in a proper case, an "involuntary plaintiff." Service on a person joined under this rule follows the same manner and time limits as Rule 4 governs generally — a distinctly local feature, since the District of Columbia has no separate venue to transfer a case to and so has no need for the federal venue provision this rule otherwise mirrors.

Sometimes a required person truly cannot be joined — perhaps the court has no way to reach them. Rule 19(b) then asks the court to weigh, in equity and good conscience, whether the case should proceed among the existing parties or be dismissed instead. The court looks at how much a judgment reached without the absent person might prejudice that person or the existing parties, whether protective terms in the judgment or a reshaped form of relief could reduce that prejudice, whether a judgment issued without them would still be adequate, and whether the plaintiff would have another adequate remedy if the case were dismissed. Rule 19(c) requires a party to name any known required person it has left out of the case and explain why, and Rule 19(d) makes the whole rule give way to Rule 23, which has its own machinery for deciding who is bound in a class action.