Law 101 for Experts: What Can and Cannot Be Asked of an Expert Witness at Trial

Any expert witness who has given trial testimony or watched another expert on the stand may think questioning is a free for all.

Dani Alexis Ryskamp, J.D.

Written by
— Updated on July 12, 2022

Law 101 for Experts: What Can and Cannot Be Asked of an Expert Witness at Trial

While lawyers aren’t limited to a particular script at trial, they aren’t given total latitude, either. The Federal Rules of Evidence (FRE) and similar rules in state courts govern what attorneys can and cannot ask an expert witness at trial.

Experts can benefit from understanding how the rules of evidence apply. These rules help experts spot patterns and identify potentially problematic questions.

How the Rules of Evidence Affect the Presentation of Testimony at Trial

Federal Rule of Evidence 702 guides much of an expert witness’s testimony at trial. FRE 702 states that a witness may testify as an expert if:

  • The witness’s specialized knowledge “will help the trier of fact to understand the evidence or to determine a fact in issue”
  • The testimony “is based on sufficient facts or data
  • The testimony “is the product of reliable principles and methods”
  • The witness has applied these “reliable principles and methods” in a reliable manner to the facts in the case

In short, the recognition of an expert witness happens only after the expert does the work required to analyze some aspect of the case according to their own specialized knowledge. Once established as an expert, a witness may testify to facts related to the case. Additionally, an expert may testify to an opinion the expert has formed based on their analysis.

FRE 703 further explains how an expert witness may testify to an opinion. For example, experts may base their opinion on facts or data they have “been made aware of or personally observed.” Under FRE 705, experts may testify to their opinion first or to the underlying facts or data first.

What You Say vs. What the Jury Hears 

In addition to the rules for expert testimony, experts also must follow the rules that govern witness testimony generally. These rules also have an impact on what expert witnesses may say. Additionally, these rules impact what testimony the expert presents to or keep from the jury.

An attorney preparing to question a witness considers several factors, including:

  • Relevance. FRE 403 and similar state court rules require evidence to be relevant to the questions before the court. The court may exclude relevant evidence, however, if it is more likely to prejudice or confuse the jury than it is to help them understand the case.
  • Privilege. FRE 502 addresses attorney-client privilege, especially relating to work product. Privilege may be an issue if a lawyer consults with an expert witness and only later the lawyer asks the expert to take the stand. The consultation work may be classified as a privileged work product—or it may not.
  • Hearsay. To be hearsay, the testimony must be (1) an out-of-court (2) statement (3) made to establish the truth of what the expert asserted in the statement. Hearsay is generally inadmissible. However, many exceptions apply, and the court excludes some types of testimony from the hearsay rules.
  • Prior Motions and Rulings. The court uses a motion in limine to exclude certain evidence, testimony, or topics from trial. Attorneys plan their questioning with any results from prior proceedings, like a motion in limine or a Daubert hearing for an expert witness, firmly in mind.

These rules apply to all types of witnesses. As such, they shape how attorneys question experts—both their own and an opposing party’s experts. 

How the Rules Affect the Questions Lawyers Ask

The rules of evidence shape attorneys’ questioning of expert witnesses in several ways.

The rules require the attorney to establish a witness as an expert before the expert offers an opinion. As such, attorneys will typically begin by working through the expert’s credentials and experience. This process can feel tedious to an expert, but it is essential for the judge and jury.

FRE 705 allows experts to testify to their opinion and to the facts that underlie it in any order. During direct examination, an attorney may ask about the facts and data before the opinion, after the opinion, or not at all. An expert witness who the lawyer didn’t ask during direct examination about the underlying facts and data, however, should prepare to answer questions about them during cross-examination.

Direct and cross-examination each have their own rules as well, which shape which questions attorneys ask and how. For example:

  • Direct examination tends to include more open-ended questions, such as “What did you find when you examined ___?”
  • Cross-examination relies more heavily on leading questions or questions that imply their own answer, such as “When you examined ___, you found __, isn’t that right?”
  • An attorney conducting cross-examination is typically limited to the topics raised during direct examination. A seemingly off-topic question is permitted, however, if the attorney can show it leads to a raised topic or issue (and it adheres to other applicable rules).


Attorneys use objections to keep one another within the bounds of the rules. An expert witness can assist with this process by pausing briefly after an attorney asks a question. This pause gives an attorney time to raise any applicable objection to the question.

The court may sustain some objections. As such, it’s important not to answer an objected-to question until directed to do so. A jury that never hears an answer to an impermissible question can more easily focus on the expert’s opinion than a jury that heard the answer and then the court tells the jury to ignore it.

The process of eliciting and giving testimony is a highly structured, specialized form of storytelling. The Rules of Evidence govern the form and content of the story, which attorneys and witnesses direct and build together. By understanding these rules, expert witnesses can contribute more effectively to the overall story of the case.

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