- Rule 20(a)(1 & 2): -- Right to relief must be asserted by each plaintiff, or against each defendant -- Arising out of the same transaction or occurrence, or series of transactions or occurrences, and -- Common question of law or fact - Rule 20(a)(3): -- Neither a plaintiff nor a defendant need be interested in obtaining or defending against all the relief demanded. The court may grant judgment to one or more plaintiffs according to their rights, and against one or more defendants according to their liabilities