You’ve studied jurisdiction, pleadings, and discovery backwards and forwards — but then an MBE question drops a fact pattern about expert witness disclosure, and suddenly you’re second-guessing everything you thought you knew about civil procedure.

That’s not an accident. Expert witness disclosure is one of those topics that sits quietly in the Federal Rules until the exam decides to make it the entire issue. If you don’t know the specific requirements cold, you’ll miss points that you absolutely should not be missing.

Here’s what you need to know.

What Expert Witness Disclosure Actually Is

Under the Federal Rules of Civil Procedure, expert witness disclosure is a mandatory pretrial obligation. It’s part of the broader discovery framework under FRCP 26, which governs what parties must share with each other — and when — without waiting for someone to ask.

The core idea is straightforward: if you plan to use an expert witness at trial, the other side is entitled to know who that person is and what they’re going to say, well before anyone walks into a courtroom. The rule distinguishes between two types of experts, and that distinction is tested heavily on the MBE.

Two Types of Experts: Know the Difference

The FRCP draws a clean line between retained or specially employed experts and non-retained experts, and the disclosure obligations are different for each.

A retained expert is someone you hired specifically to provide expert testimony — think a forensic accountant, a medical expert, or an accident reconstruction specialist brought in for the case. These witnesses carry the heaviest disclosure burden.

A non-retained expert is someone like a treating physician who may offer expert opinions but wasn’t brought in specifically to testify. Their disclosure obligations are lighter.

On the MBE, a question might describe a witness and ask whether a full written report is required. The answer turns entirely on which category that witness falls into.

The Written Report Requirement

For retained or specially employed experts, FRCP 26(a)(2)(B) requires a written report signed by the witness. This is not optional, and the MBE will test whether you know what goes inside it.

The report must contain:

Every single one of those elements is fair game for a bar exam question. A common MBE trap is a question where the expert’s report is missing one element — say, the compensation disclosure — and you have to identify whether the disclosure was proper. It wasn’t.

Non-Retained Expert Disclosure: Less, But Still Required

For non-retained experts, FRCP 26(a)(2)(C) requires a disclosure that includes the subject matter on which the witness is expected to present evidence and a summary of the facts and opinions to which the witness is expected to testify. No full written report is required.

This comes up in MBE fact patterns involving treating physicians. If a doctor treated the plaintiff after a car accident and will testify about the injuries observed and the prognosis given, that doctor likely qualifies as a non-retained expert. The disclosure is simpler — but it still must happen.

Don’t confuse “no report required” with “no disclosure required.” That’s a trap the exam loves.

Timing: When Does Disclosure Have to Happen?

Expert witness disclosure timing is another area where the MBE likes to create confusion. Under FRCP 26(a)(2)(D), expert disclosures must be made at the times and in the sequence that the court orders. If the court hasn’t set a schedule, the default rule kicks in: disclosures must be made at least 90 days before the date set for trial or for the case to be ready for trial.

There’s an important wrinkle. If the evidence is intended solely to contradict or rebut another party’s expert, the disclosure deadline is 30 days after the other party’s disclosure. So if the plaintiff discloses an expert, the defendant has 30 days from that point to disclose a rebuttal expert — not 90 days from trial.

That 90-day versus 30-day distinction is exactly the kind of specific number the MBE will test. Know both.

What Happens When Disclosure Is Defective or Late?

This is where civil procedure and evidence overlap, and it’s where MBE questions can get layered.

Under FRCP 37(c)(1), if a party fails to provide required expert disclosure information, that party is not allowed to use the undisclosed expert or information at trial, at a hearing, or on a motion — unless the failure was substantially justified or harmless.

Courts consider several factors in making that determination, including whether the other party was surprised or prejudiced, whether the deficiency could be cured, and whether allowing the testimony would disrupt the trial.

On the MBE, you might see a question where a party tries to introduce expert testimony at trial and the opposing party objects because the disclosure was untimely. The question asks whether the court should exclude the testimony. The answer depends on whether the failure was substantially justified or harmless — and the exam will usually give you facts that point clearly one way or the other.

A Quick Hypothetical

Consider this: Plaintiff sues a pharmaceutical company for product liability. Plaintiff discloses a retained pharmacology expert 95 days before trial and provides a written report. The report includes the expert’s opinions, qualifications, and the data considered, but omits the list of prior cases in which the expert has testified.

Is the disclosure sufficient?

No. Even though the timing is fine — 95 days exceeds the 90-day minimum — the written report is deficient because it’s missing a required element. The defendant could move to exclude the expert’s testimony under FRCP 37(c)(1), and the court would likely grant it unless the plaintiff could show the omission was harmless or substantially justified.

That’s a clean MBE-style issue. One element missing. One clear consequence.

Supplementing Expert Disclosures

One more rule you need: supplementation. Under FRCP 26(e), a party who has made an expert disclosure must supplement that disclosure in a timely manner if the party learns the information disclosed is incomplete or incorrect, and if the additional or corrective information has not otherwise been made known to the other parties.

This duty to supplement is ongoing. It doesn’t end when the initial disclosure is filed. And if you fail to supplement and then try to use the new information at trial, FRCP 37(c)(1) applies the same exclusion sanction.

FlashTables is a set of professionally formatted two-column PDF rule tables covering all seven MBE subjects — 704 rules total, organized by the official NCBE Subject Matter Outline. The expert witness disclosure rules covered in this article are laid out side-by-side in the Civil Procedure table, so you can see the retained versus non-retained distinction, the report elements, and the timing requirements all at a glance. Whether you’re a law student locking in black-letter civil procedure for finals or a bar-taker drilling active recall in the final weeks before the MBE, the tables are built for exactly that kind of focused repetition.

Key Takeaways: What to Memorize for Expert Witness Disclosure

Before you move on, make sure these are locked in:

If you want to review these rules alongside the rest of the Civil Procedure subject matter outline in one organized reference, FlashTables has the Civil Procedure table and all six other MBE subjects ready to go.