§ 387.Generally
Title 3. Of the Parties to Civil Actions · Chapter 7. Intervention · Last amended 2018 · Last verified July 28, 2026
Full Text of § 387
Plain-English Summary
Intervention lets someone who is not yet a party join a case that other people already started. Subdivision (b) describes the three ways a nonparty, called an intervenor, can do it: by joining a plaintiff in claiming what the complaint seeks, by uniting with a defendant to resist the plaintiff’s claims, or by asserting something adverse to both the plaintiff and the defendant.
Subdivision (c) sets the procedure: the nonparty must petition the court for leave to intervene, by noticed motion or ex parte application, attaching a proposed complaint or answer in intervention and stating the grounds for intervening. Subdivision (d) then splits intervention into two tracks. The court must grant intervention when either a statute confers an unconditional right to intervene, or the nonparty claims an interest in the property or transaction at issue and is situated such that the case’s disposition may impair or impede that interest, unless an existing party already represents it adequately. Short of that, the court may grant permissive intervention whenever the nonparty has an interest in the matter in litigation, in the success of either party, or against both.
Subdivisions (e) and (f) cover what happens once intervention is granted: the intervenor must separately file its complaint or answer in intervention, and serve it on the other parties in the same manner as a summons — or, for a party who has already appeared, in that same manner or under the mail-service rules of Chapter 5 (commencing with § 1010) of Title 14. The existing parties then get 30 days after service to move, demur, or otherwise plead to the intervenor’s pleading, just as they would to an original complaint or answer.
Frequently Asked Questions
What is the difference between intervention and interpleader?
Intervention lets an outsider join someone else’s already-pending lawsuit under § 387; interpleader under § 386 lets a stakeholder holding disputed money or property force competing claimants to litigate against each other in a case the stakeholder itself brings or defends against.
When is a court required to let someone intervene?
Under § 387(d)(1), intervention is mandatory when a statute confers an unconditional right to intervene, or when the nonparty’s interest in the property or transaction at issue could be impaired by the case’s outcome and no existing party adequately represents that interest.
Can a court allow intervention even without an unconditional right to it?
Yes. § 387(d)(2) gives the court discretion to permit intervention whenever the nonparty has an interest in the matter in litigation, in the success of either party, or against both.
How does someone ask to intervene in a California case?
§ 387(c) requires a petition for leave to intervene, by noticed motion or ex parte application, including a copy of the proposed complaint or answer in intervention and the grounds for intervening.
Once a court grants intervention, how much time do the existing parties have to respond?
§ 387(f) gives the parties 30 days after service of the complaint or answer in intervention to move, demur, or otherwise plead to it, the same as they would to an original pleading.
Amendment History
Amended by Stats 2017 ch 131 (AB 1693),s 1, eff. 1/1/2018.