Rule 33.Intervention

Intervention lets someone outside a lawsuit step into it — joining the plaintiff’s side, the defendant’s side, or asserting a claim against both. Rule 33 recognizes two paths in. Intervention of right applies when a statute, one of these rules, or the common law gives the person an unconditional right to join; the court has no discretion to keep them out. Permissive intervention applies when the person has an interest in the matter being litigated; there, the court decides whether to let them in, weighing whether the intervention would unduly delay the case or prejudice the parties already in it. Both paths share the same deadline: the motion must come before trial.

Getting in takes more than asking. The person who wants to intervene must serve a motion to intervene on the existing parties the same way any motion is served under Rule 9, state the grounds for intervening, and attach a proposed pleading laying out the claim or defense they want to raise. If the court grants the motion, the existing parties then have 10 days to file whatever responsive pleadings these rules would otherwise require or allow.