How to File a Motion to Intervene in California: Section 387 Steps

To file a motion to intervene in California, prepare a notice of motion, a complete proposed pleading, and a memorandum of points and authorities under Code of Civil Procedure Section 387, file the package with the Superior Court handling the case, pay the first-appearance filing fee, and serve every existing party at least 16 court days before the hearing.¹ The steps below walk through each piece in the order you’ll handle them.

Confirm You Qualify Under Section 387

Before you draft anything, figure out which type of intervention your situation fits. The answer shapes your memorandum and tells you how much latitude the judge has.

Intervention of Right

The court must grant your motion if you meet all three conditions: you have a stake in the property or transaction at the heart of the lawsuit, the outcome could impair your ability to protect that stake, and the existing parties don’t adequately represent your position.¹ Clear all three and the judge has no discretion to refuse.

A separate statute can also give you an unconditional right to intervene in a particular kind of case.¹ Government agencies sometimes hold these rights under specific regulatory or environmental statutes. When a statute puts you in by name, the three-part test doesn’t apply.

Permissive Intervention

If mandatory intervention doesn’t fit, you can ask the court to let you in as a matter of discretion. The statute allows this when you have an interest in the subject matter of the lawsuit, an interest in the success of one of the parties, or an interest against both sides.¹ The threshold is lower, but the judge will weigh your reasons against potential delay, prejudice to the existing parties, and unnecessary expansion of the issues.

File on Time

Both paths require a “timely application,” and this is where many motions die. California sets no fixed deadline. Courts look at the circumstances and ask whether you waited too long after learning the lawsuit could affect you.¹

Judges regularly deny motions filed after the existing parties have reached a comprehensive settlement, because jumping in at that stage prejudices people who’ve already invested time and money. File as soon as you learn the lawsuit could affect your interests. Every week of unexplained delay is a week you’ll have to justify.

Assemble the Three Documents

Your filing package has three components, and all of them need to be fully prepared before you submit anything.¹

Notice of Motion

The cover document. It identifies the case, states the hearing date and courtroom, and puts the parties on notice that you’ll be seeking party status on a specific day. It also starts the clock on opposition papers.

Proposed Pleading

Attach a complete, ready-to-file pleading to the motion. If you’re aligning with the plaintiff, that’s a complaint in intervention. If you’re joining the defense, it’s an answer in intervention.¹ Not a draft or outline. The court expects a finished document that could be filed the moment the motion is granted, with the claims or defenses clearly laid out.

Memorandum of Points and Authorities

Your legal argument. Explain the facts behind your interest, identify which type of intervention applies, and cite the statutory language and case law supporting your position. Most practitioners attach supporting declarations as well, with sworn statements from people who have firsthand knowledge of the facts and can address why the existing parties can’t adequately protect your interest. The declarations give the court the evidentiary record it needs to rule.

File the Package and Pay the Fee

Submit the complete package to the Superior Court where the original case is pending. Because this is your first appearance, you owe the first-appearance filing fee. For unlimited civil cases, where the amount at stake exceeds $35,000, that fee is $435 as of January 2026.² Limited civil fees are lower:

Over $10,000 up to $35,000: $370
$10,000 or less: $225

Riverside, San Bernardino, and San Francisco counties add local courthouse construction surcharges.² Government entities may be exempt entirely under Government Code Section 6103.

Serve Every Existing Party

Once the package is filed, serve it on every existing party. Faulty service can get the motion thrown out before the judge reads a word of substance.

Under CCP 1005(b), moving and supporting papers must be served at least 16 court days before the hearing.³ Serving by mail or other non-personal methods adds calendar days to that baseline:

Mail within California: add 5 calendar days
Mail to or from outside California but within the U.S.: add 10 calendar days
Overnight delivery or fax: add 2 calendar days

After serving, file a proof of service with the court identifying who was served, when, and how.³ Without it, the hearing won’t go forward.

Section 387(c) allows an ex parte application in place of a noticed motion when genuine urgency demands a faster timeline.¹ Courts expect a real emergency, such as an imminent deadline or a hearing that could moot your interests, not just a preference to move faster.

What to Expect at the Hearing

The judge reviews the papers and hears argument from you and the existing parties. For mandatory intervention, the analysis is straightforward: if your papers establish the required interest, impairment, and inadequate representation, the court grants the motion.

Permissive hearings involve more back-and-forth. Existing parties typically argue that your participation will slow the case, broaden the issues, or duplicate work. Your job is to show that your interest is real enough to justify whatever complexity you add. Courts are more receptive early, before extensive discovery and motion practice have shaped the case.

After the Ruling

If the court grants the motion, the order alone doesn’t put your pleading into the record. You have to separately file the complaint or answer in intervention that was attached to the motion. You also need to serve both the order and your filed pleading on all parties. Parties who haven’t yet appeared require formal personal service, the same method used for an original summons. Parties who have appeared can be served by that method or by standard mail or electronic means.¹ Once in, you’re a full party and bound by the judgment, and the court won’t reset deadlines because you arrived late to the case.

If the motion is denied, your appellate route depends on which type you sought. A denial of mandatory intervention is generally treated as a final judgment against you for purposes of appeal, so you can take a direct appeal to the Court of Appeal. Denials of permissive intervention are harder to challenge and typically require a petition for a writ of mandate asking a higher court to review whether the trial court abused its discretion. If intervention is off the table, participating as amicus curiae remains an option for influencing the court’s reasoning without becoming a party.

1
California Legislative Information. California Code of Civil Procedure CCP 387 – Intervention
2
Judicial Branch of California. Statewide Civil Fee Schedule Effective January 1, 2026
3
California Legislative Information. California Code of Civil Procedure CCP 1005