To write an amicus brief that a federal appellate court will accept, you need to offer the court something the parties have not already said, secure permission to file (or confirm all parties consent), follow the required structure and disclosures under Federal Rule of Appellate Procedure 29, stay within the word limit, and file within seven days of the principal brief of the party you support. Everything else is detail hanging off those requirements.
The guidance below focuses on federal appellate practice, where the clearest rules exist, with a separate section on the U.S. Supreme Court. State appellate courts have their own local rules; check them before you file anywhere else.
Start by Finding What Is Missing
Before drafting, pull the full record from the lower court. Read the trial court’s decision, the questions presented on appeal, and every brief the parties have already filed. The point of this reading is not to absorb the case; it is to find the gap.
An amicus brief exists to tell the court something it would not otherwise hear. A brief that restates one party’s arguments is a “me too” brief, and courts either reject it or ignore it. Your contribution usually falls into one of a few shapes: empirical data the parties lack, historical or technical context they glossed over, or an analysis of how the ruling will affect an industry, profession, or community the parties did not speak for. If you cannot articulate the gap in a sentence, you do not yet have a brief worth filing.
Secure Permission to File
Federal appellate courts do not automatically accept amicus briefs from private filers. You need either the consent of all parties or leave of the court.1Legal Information Institute. Federal Rules of Appellate Procedure Rule 29 – Brief of an Amicus Curiae
If every party consents, you skip the motion process; the brief simply states that all parties agreed. Many parties grant blanket consent because publicly opposing an amicus filing tends to look bad.
If any party withholds consent, file a motion for leave to file. The motion must explain your interest in the case and why your brief would help the court. You submit the completed brief with the motion so the court can evaluate both at once. A persuasive motion typically shows that the parties cannot fully present the relevant considerations themselves, that you can point to law or arguments the court might otherwise miss, or that your brief would genuinely assist the court in reaching a sound decision.
The United States, its agencies, and state governments can file without consent or leave.
File Within Seven Days
In federal appellate courts, an amicus brief must be filed no later than seven days after the principal brief of the party you support.1Legal Information Institute. Federal Rules of Appellate Procedure Rule 29 – Brief of an Amicus Curiae If you are supporting the petitioner, your clock runs from the date the petitioner files their opening brief. Courts routinely reject late filings. Plan backward from the expected filing dates and build in a buffer.
A separate, shorter deadline applies if you want to file during the court’s consideration of rehearing or rehearing en banc, and the word cap at that stage drops to 2,600.
Build the Required Structure
Federal appellate courts expect a specific architecture. Deviate from it and the clerk’s office may bounce the filing before a judge ever sees it.
Cover Page
Identify which party you support and whether you are asking the court to affirm or reverse.1Legal Information Institute. Federal Rules of Appellate Procedure Rule 29 – Brief of an Amicus Curiae If you support neither side, say so. The cover also carries the case name, docket number, court name, and the title “Brief of [Name] as Amicus Curiae.”
Tables and Corporate Disclosure
Include a table of contents with page references and a table of authorities listing every case, statute, and source cited (cases alphabetically). A corporate amicus must also include a corporate disclosure statement. These sections are mechanical, but they are mandatory.
Statement of Identity and Interest
Introduce yourself to the court. Explain who you are, why you care about the case, and what qualifies you to offer a useful perspective. An industry association should describe its membership; an academic should summarize the relevant expertise. Keep it tight. Judges want to know why they should listen, not read your résumé.
Argument
This is the heart of the brief. Present your unique information, research, and legal analysis here. A summary of the argument at the beginning is permitted but not required.1Legal Information Institute. Federal Rules of Appellate Procedure Rule 29 – Brief of an Amicus Curiae Unlike a party’s brief, an amicus brief does not need to include a statement of the standard of review. Spend your words on what the parties cannot or did not say.
Conclusion
State the outcome the court should reach, usually affirmance or reversal. Keep it short. The conclusion is not the place to reargue the case.
Make the Required Disclosures
Private amicus filers must disclose three things in the brief: whether a party’s counsel authored the brief in whole or in part, whether a party or a party’s counsel contributed money to fund the brief’s preparation or submission, and whether any other person besides the amicus, its members, or its counsel contributed money for those purposes.1Legal Information Institute. Federal Rules of Appellate Procedure Rule 29 – Brief of an Amicus Curiae If the answer to any of these is yes, identify the contributor. These rules exist to prevent parties from quietly funding amicus briefs to simulate broader support. Omitting the disclosures is one of the fastest ways to get a brief rejected.
Respect Word Limits and Formatting
An amicus brief in federal appellate court can be no longer than half the maximum length allowed for a party’s principal brief.1Legal Information Institute. Federal Rules of Appellate Procedure Rule 29 – Brief of an Amicus Curiae A principal brief maxes out at 13,000 words, so the standard amicus cap is 6,500 words.2Legal Information Institute. Federal Rules of Appellate Procedure Rule 32 – Form of Briefs, Appendices, and Other Papers At the rehearing stage, the cap is 2,600 words. Courts can grant permission to exceed these limits. Do not count on it.
Formatting follows Federal Rule of Appellate Procedure 32: a proportionally spaced 14-point font such as Century Schoolbook, or a monospaced font with no more than 10.5 characters per inch, plus specified margins, binding, and paper size.
File and Serve the Brief
Most federal appellate courts use the CM/ECF electronic filing system. Register for an account if you do not already have one, then upload the brief (and the motion for leave, if required) through the system, which timestamps the filing and notifies the court.
You must also serve a copy on every party. In courts using CM/ECF, electronic filing typically satisfies service for attorneys registered in the system because the system sends automatic notifications. For any party not registered, or any party appearing without a lawyer, serve a paper copy by personal delivery, first-class mail, or a commercial carrier that delivers within three days. Include a certificate of service at the end of the filing describing how and when you served each party.
After filing, the court will issue an order granting or denying leave. A denial ends the brief’s role in the case.
If You Are Filing in the U.S. Supreme Court
Supreme Court practice differs in several ways that catch first-time filers.
Consent, Notice, and Who Is Exempt
The Court requires written consent of all parties or leave of court. Parties can file blanket consent letters with the Clerk’s Office, and many do. Government entities filing through the Solicitor General, a state attorney general, or an authorized local government law officer are exempt from the consent requirement.3Legal Information Institute. Supreme Court Rules Rule 37 – Brief for an Amicus Curiae
At the petition and opposition stage, you must give counsel for all parties at least 10 days’ notice of your intention to file before the brief’s due date. The notice requirement does not apply at the merits stage.4Supreme Court of the United States. Rules of the Supreme Court of the United States
Word Caps
- Petition stage: 6,000 words.5Supreme Court of the United States. Memorandum to Those Intending to File an Amicus Curiae Brief
- Merits stage, private filers: 8,000 words.
- Merits stage, government entities: 9,000 words.
Footnotes count toward the limit.
Booklet Format and Cover Color
The Court requires briefs in booklet format with color-coded covers. Amicus briefs at the petition stage use cream. At the merits stage, briefs supporting the petitioner or neither party use light green; briefs supporting the respondent use dark green.6Legal Information Institute. Supreme Court Rules Rule 33 – Document Preparation: Booklet Format; 8 1/2- by 11-Inch Paper Format Briefs filed by the Solicitor General for the United States use gray. The wrong color is a surprisingly common filing delay.
What Gets Briefs Rejected
Courts deny motions for leave, or strike accepted briefs, for a handful of recurring reasons. The most common is untimeliness: miss the deadline by a day and the brief is done. The second is failing to offer anything new, which signals to the court that the brief is padding the record rather than helping it.
Procedural defects do the rest. Missing disclosures, exceeding the word limit, using the wrong format, or failing to serve all parties can each independently sink the filing. Before you file, check every procedural requirement against the specific court’s rules, run an accurate word count, and confirm every required section is present. The strength of your argument does not matter if the brief never makes it past the clerk’s office.
One Boundary Worth Noting
No specific federal rule governs amicus participation at the district court level, so whether to allow a brief there falls to the presiding judge’s discretion. If you are hoping to weigh in at a federal trial, do not assume the appellate rules above apply; ask the court what it will accept, and when.