Federal Rule of Evidence 703

What the rule says

FRE 703 answers a different question from FRE 702. Rule 702 asks whether an opinion is admissible. Rule 703 asks what the opinion may be built out of, and what the jury may be told about it. Its current text took effect 1 December 2011:

“Rule 703. Bases of an Expert’s Opinion Testimony. An expert may base an opinion on facts or data in the case that the expert has been made aware of or personally observed. If experts in the particular field would reasonably rely on those kinds of facts or data in forming an opinion on the subject, they need not be admissible for the opinion to be admitted. But if the facts or data would otherwise be inadmissible, the proponent of the opinion may disclose them to the jury only if their probative value in helping the jury evaluate the opinion substantially outweighs their prejudicial effect.”

Three sentences, and each does separate work: what an opinion may rest on, when inadmissible material qualifies, and what may be repeated in front of the jury.

Three sources, one of which needs a justification

The first sentence permits an opinion to rest on facts or data the expert personally observed — the examination, the inspection, the testing done in the engagement — or that the expert has been made aware of, which covers the case file counsel produced, the deposition transcripts, the documents produced in discovery, and the materials the expert asked for and received.

The second sentence adds the category that makes the rule worth arguing about: material that would not itself be admissible. Industry data compilations, published surveys, another professional’s report, records assembled by someone who will not testify, treatises — a great deal of what any competent professional works from is hearsay. Rule 703 permits an opinion to rest on it, on one condition, and does not require that the material ever come into evidence.

What the rule does not do is make the material itself admissible. It creates no hearsay exception. The opinion comes in; the underlying document stays out unless some other rule lets it in or the third sentence is satisfied. Losing that distinction is the most common misreading of the rule, and it produces the argument that an expert may rely on anything.

A second distinction runs through every argument under the rule: the difference between what an expert was given, what the expert reviewed, and what the opinion actually rests on. Only the third is the basis for Rule 703 purposes. A file that arrives from counsel with several thousand pages in it is not thereby the basis of anything, and an expert who describes the entire production as the basis has made the reliance question harder to defend, not easier — because reasonable reliance then has to be established for material the opinion never used. Identifying the basis narrowly and accurately is the proponent’s interest as much as the opponent’s.

Reasonable reliance is measured by the field, not by the witness

The condition is objective and external: whether experts in the particular field would reasonably rely on those kinds of facts or data in forming an opinion on the subject. Two features of that phrasing carry weight.

The referent is the field, not the individual. That this expert customarily relies on a source establishes nothing; the question is what a competent practitioner in the discipline would do. And the object of the inquiry is the kind of material rather than the specific document, which is why the argument is usually about categories — whether practitioners in the field rely on self-reported data of this type at all — rather than about the reliability of one particular record.

Reasonable reliance is a preliminary question for the court under FRE 104(a), decided on the same preponderance standard that governs Rule 702. It is not a question the expert answers by asserting it, although the expert’s testimony about the practice of the field is evidence going to it. Where the field’s own conventions are contested, or where the witness relies on something the field does not, the objection is available under Rule 703 independently of any Rule 702 attack.

The disclosure sentence runs Rule 403 backwards

The third sentence is the part that decides what a jury hears, and it inverts the ordinary balance. Under FRE 403 relevant evidence is admitted unless its probative value is substantially outweighed by the danger of unfair prejudice — a presumption in favor of admission. Under Rule 703, otherwise inadmissible basis material may be disclosed to the jury only if its probative value in helping the jury evaluate the opinion substantially outweighs its prejudicial effect. The presumption is reversed, and the proponent has to earn the disclosure.

Two further limits are built into the same sentence. The probative value that counts is a specific one — value in helping the jury evaluate the opinion, not value as substantive proof of the fact asserted. And the restriction runs against the proponent of the opinion. This reversed balance was added to the rule effective 1 December 2000.

The structural risk it addresses is easy to state. Rule 703 permits an opinion to be built on material the rules of evidence keep out. If the witness could then recite that material from the stand as the reasons for the opinion, the rule would function as a channel through which excluded evidence reaches the jury with a qualified professional’s endorsement attached to it — and with the person who created it never subject to cross-examination. Restricting disclosure rather than reliance is what keeps the permission in the second sentence from consuming the exclusionary rules the material failed in the first place.

How this interacts with the order of proof

FRE 705 supplies the sequence: “Unless the court orders otherwise, an expert may state an opinion — and give the reasons for it — without first testifying to the underlying facts or data. But the expert may be required to disclose those facts or data on cross-examination.” The mandatory hypothetical question, which once forced a proponent to put the entire factual predicate in front of the jury before the opinion could be given, is gone.

The consequence is that the underlying material is normally drawn out by the opponent rather than volunteered by the proponent, which is a strategic problem as often as an opportunity: cross-examination that walks a jury through a weak basis also puts that basis in front of them, with the expert given the opportunity to explain it. Where the material is inadmissible and the opponent elicits it, courts commonly instruct that it is admitted to show the basis for the opinion rather than for its truth.

Where the rule is unsettled

The recurring difficulty is the conduit problem: how aggressively a court should police an expert’s recitation of otherwise inadmissible material as basis, when the practical effect of the recitation is to put the substance before the jury. Courts differ in how far they will let a witness go, and a limiting instruction is an imperfect answer to the difficulty because it asks a jury to use a document to evaluate an opinion while not treating it as evidence of what it says.

In criminal cases the question intersects with the Confrontation Clause, which adds a constitutional dimension to what is otherwise an evidentiary balance. The dividing line between an expert who has genuinely applied independent judgment to material and one who is transmitting another person’s conclusions is doing a great deal of work there, and it is not sharply drawn.

What the rule means for an opponent

Rule 703 is the opponent’s rule in the sense that it is rarely litigated unless someone raises it. A proponent who is comfortable that the basis is conventional in the field will not brief the point at all, and it can pass unexamined through disclosure and deposition.

The two available objections are distinct and are often confused. The first goes to reliance: that practitioners in this field would not reasonably rely on this kind of material, which if sustained undercuts the opinion itself and overlaps with the requirement in FRE 702(b) that the testimony be based on sufficient facts or data. The second goes only to disclosure: the reliance may be proper while the recitation of the material to the jury fails the reversed balance. The second objection leaves the opinion standing and changes what the jury hears, which is sometimes the more realistic aim.

The record for either is built at deposition, from what the expert asked for, what was supplied, what was reviewed and what was relied on — a distinction the disclosure rules and the report requirement force into the open. Primary text: Rule 703 and Rule 705.

Frequently Asked Questions

Published 2026-08-12