Rule 20.Permissive Joinder of Parties

Rule 20(a) sets a two-part test for joining plaintiffs or defendants who were not required to be joined under Rule 19. On the plaintiffs' side, multiple people can join in a single suit if they assert a right to relief, whether joint, several, or in the alternative, arising from the same transaction, occurrence, or series of transactions or occurrences, and if some question of law or fact common to all of them will come up in the case. The same test runs in reverse for defendants: they can be joined together if a right to relief is asserted against them arising from the same transaction or series of transactions, with a common question running through the claims against them. Neither a joined plaintiff nor a joined defendant has to be interested in every piece of relief sought in the case, and the court can enter judgment for some plaintiffs and against some defendants according to each one's actual rights and liabilities, without treating the group as an all-or-nothing unit.

Because permissive joinder can pull together parties whose connection to each other is real but partial, section (b) gives the court tools to keep that arrangement fair. If including a particular party would embarrass, delay, or run up costs for someone who has no claim against them and against whom they assert none, the court can enter whatever orders prevent that harm, including separate trials.

Rule 20 differs from Rule 18 in what it governs: Rule 18 controls how many claims a single party can bring against another, with almost no limit, while Rule 20 controls when multiple parties can be gathered into one lawsuit in the first place, and requires the transaction-and-common-question link before that gathering is allowed.