Expert witnesses have become indispensable to modern litigators: from providing key testimony in major cases involving mergers and acquisitions to guiding municipal regulators on environmental standards, their presence and specialization may be the key to achieving desired results. Attorneys should be familiar with professional and ethical rules that govern interactions between lawyers and experts. This article outlines some of those issues as discussed by the American Bar Association (ABA) in accordance with its Model Rules for Professional Conduct. See, e.g., Neil J. Wertlieb, “Ethics Issues in the Use of Expert Witnesses,” The Professional Lawyer, 2016, Vol. 24, No. 3.


There are a number of factors attorneys should consider in understanding what ethical rules apply to their relations with experts, and each jurisdiction has its own code for professional responsibility. The American Bar Association Model Rules are a good starting point, as many states adopt such provisions in whole or in part, and they provide general concepts to help litigators understand the overarching policy goals they embody. What follows are some of the more common questions/issues lawyers may encounter in dealing with expert witnesses.

(1). Fees: ABA Model Rule 3.4 contains a comment that addresses certain fee arrangements between lawyers and experts and expresses that “it is not improper to pay a witness’s expenses or to compensate an expert witness on terms permitted by law. The common law rule in most jurisdictions is that it is improper to pay an occurrence witness any fee for testifying and that it is improper to pay an expert witness a contingent fee.” Id., citing ABA Rule 3.4, Comment [3]. Most jurisdictions follow this rule and do not allow experts to be paid on a contingent basis. See id.This rule has been adopted officially by the Second Circuit Court of Appeals, which also held that “experts should be unbiased and objective witnesses, not swayed by the incentive of receiving a higher payout if their testimony is ‘successful.’”Id.

Although this rule may appear straightforward, the ABA has explained that while the rule applies to testifying expert witnesses, consulting experts may be treated differently. See id.The ABA concludes that with respect to non-testifying experts, “because the prohibition relates to witnesses, it probably does not prohibit contingency fees to consulting experts who do not testify.” Id.

(2). Candor to the Court: Just as attorneys have a duty not to suborn false statements with respect to their clients, they have an analogous obligation with testifying experts. See, e.g., id.A lawyer cannot, under ABA Model Rule 3.2, “actively procure or knowingly countenance the commission of perjury …. Knowingly offering as genuine and true a written instrument fraudulently antedated and fraudulently fabricated is equally reprehensible.” Id.If an expert witness were to make a false statement of material fact or provide an opinion or evidence that an attorney knows is fraudulent, that attorney must abide by the same duties that would be owed in their professional rules regarding candor to a tribunal/court. See, e.g, id.Litigators cannot countenance evidence or testimony that they know to be false.

(3). Adverse Experts: ABA Rule 3.4 governs fairness to opposing counsel, parties, and actors. See id.Certainly, most attorneys are well aware that witness tampering and intimidation tactics are prohibited, and that such prohibition extends to interactions with adverse expert witnesses. See, e.g., id.However, Rule 3.4 does not merely apply in the more extreme situations, and litigators should be aware of some of its more nuanced proscriptions. For instance, according to the ABA, “Litigators should also be cautious about contact with experts outside of the courtroom.” Id.More specifically, the Ninth Circuit Court of Appeals held that some expert testimony would be excluded because the witness had been designated by plaintiffs and had ex parte contact with the defense. See id.There may be additional ethical issues if an attorney retains an expert who was once an agent of an opposing party. See id.Attorneys should take care to ensure that no such conflicts exist and that, if an expert has been used by an adverse party, no inappropriate actions occurred within the scope of that litigation. If a prior relationship with an adverse party led to the disclosure of the retaining party’s work product, the expert may be disqualified. See id.

(4). Confidentiality: The idea of confidentiality is generally rooted in privileges invoked by attorney-client (or similar) relationships or by the work-product doctrine. See, e.g., id.In the context of experts and confidentiality, such matters are covered by the Federal Rules of Civil Procedure (FRCP) and certain formal opinions issued by the ABA. See id.In general, these rules provide that “communications with consulting experts are confidential and privileged, and their work product is not discoverable by the opposing party.” Id.,citingFRCP Rule 26(a)-(b).

If a witness begins as a consultant but later becomes a testifying expert, the situation changes, and the discovery rules that apply to testimonial expert witnesses must be followed. See id.In general, “communications with testifying experts are NOT confidential or privileged. “Id. The ABA has concurred with the FRCP and treats consulting experts in much the same way as co-counsel would be treated—they are accorded the privileges of an attorney-client relationship, and their work-product is protected. See id., citing ABA Formal Opinion 97-407.

One final aspect that attorneys may wish to be familiar with is that experts who are designated as experts but who do not actually testify may retain certain protections. See id.For example, one California Appellate Court has ruled that “[t]he designation of a party as an expert trial witness is not in itself an implied waiver of the party’s attorney-client privilege because his initial status is that of a possible expert witness. If the designation is withdrawn before the party discloses a significant part of a privileged communication . . ., or before it is known with reasonable certainty that the party will actually testify as an expert, the privilege is secure; if the party provides privileged documents or testifies as an expert…, the privilege is waived.” Shooker v. Superior Court (Winnick), 111 Cal.App.4th 923 (2003). Litigators should acquaint themselves with their jurisdictions’ rules on this matter and be able to thoroughly understand when their experts’ work and communications are confidential and when they are not.


A number of ethical issues arise whether expert witnesses are favorable or adverse.  Although each state or federal court may have somewhat varied rules, the ABA Model Rules are fairly uniform and provide an excellent starting point for attorneys to become familiar with the policies they intend to further. Criminal cases have additional rules, but for civil litigators, the preceding discussion provides an outline of some typical questions lawyers and courts may seek answers to. When attorneys retain experts, they should do their best to adhere to the professional rules and address the considerations the rules enumerate.