Rule 20.Permissive joinder of parties

Rule 20(a) sets the same two-part test for joining plaintiffs or defendants. Plaintiffs may join in one action if they assert a right to relief, jointly, severally, or in the alternative, arising out of the same transaction, occurrence, or series of transactions or occurrences, and if a question of law or fact common to all of them will arise in the action. Defendants may be joined on the same terms — a right to relief asserted against them jointly, severally, or in the alternative, out of the same transaction or series, with a common question running through the case.

A plaintiff or defendant joined under this rule doesn't have to be interested in obtaining or defending against every form of relief demanded. The court gives judgment for one or more plaintiffs according to their respective rights, and against one or more defendants according to their respective liabilities, so joinder doesn't force every party into an all-or-nothing outcome.

Rule 20(b) gives the court a counterweight to that broad joinder power. It may enter whatever orders will prevent a party from being embarrassed, delayed, or put to expense by the inclusion of a party against whom that party asserts no claim and who asserts none against it, including ordering separate trials or other orders to prevent delay or prejudice.