What your testifying expert can be asked about what you told them

Consultant or witness

The same person can hold both roles, and the protection follows the role, not the person.

A consulting expert, retained only to help counsel prepare, sits inside the privilege. Evid. Code 952 covers communications to people "to whom disclosure is reasonably necessary" for the purpose of the consultation, and the court in DeLuca read that to include communications to a consulting expert. 217 Cal.App.4th at 688. The consultant's report, prepared at counsel's request for trial preparation, is work product with conditional protection. Williamson, 21 Cal.3d at 834.

A testifying expert is different. "As a general rule, neither the attorney-client privilege nor the work product protection will prevent disclosure of statements to, or reports from, a testifying expert." DeLuca, 217 Cal.App.4th at 689. On the privilege side, the court quoted the reason: "the decision to use the expert as a witness manifests the client's consent to disclosure of the information." (Ibid., quoting Shadow Traffic Network v. Superior Court (1994) 24 Cal.App.4th 1067, 1079.)

Most retained experts start as consultants and become witnesses. That is the transition that matters.

Where the line falls

At the point it becomes reasonably certain the expert will give an opinion at trial.

The line comes from Swartzman v. Superior Court (1964) 231 Cal.App.2d 195, 203, as adopted in Williamson, 21 Cal.3d at 834-835: once it is reasonably certain an expert will testify on a material matter, the expert "has ceased to be merely a consultant and has become a counter in the litigation." DeLuca calls it a bright line, with protection before it and none after. 217 Cal.App.4th at 690.

Designation under CCP 2034.260 is the usual marker, and in Williamson the court said that once the expert was designated, "[i]ndisputedly at this point plaintiff was entitled to discover" the report. 21 Cal.3d at 835. The cases do not say designation is the only way to cross the line, and the safe reading is that anything said once you have decided to call the expert is said to a witness.

What still has protection

Written attorney impressions in a mixed report, and probably not much else.

CCP 2018.030(a) makes "[a] writing that reflects an attorney's impressions, conclusions, opinions, or legal research or theories" not discoverable "under any circumstances." National Steel applied that to a designated expert's report through a three-step in camera review: first strip out anything reflecting the attorney's thinking, which is absolutely protected; then separate advisory material, which keeps conditional protection, from the opinion the expert will give, which is discoverable; then decide whether good cause overcomes the conditional protection on the advisory part. 164 Cal.App.3d at 489-490. DeLuca restates the second step as a recognized exception for written reports. 217 Cal.App.4th at 690.

Oral communications are treated differently. In DeLuca a party argued that strategy its counsel had told a dual-role expert in conversation stayed protected after the expert testified. The court said there was no authority for that and that it was "contrary to existing law," reasoning that a conversation with a testifying witness discloses work product and that the disclosure "acts as a waiver." 217 Cal.App.4th at 691-692. The court also held, in the alternative, that the moving party had not shown what it conveyed. Id. at 692.

That leaves a question no published decision answers squarely: whether an email from counsel to a designated expert that reflects counsel's impressions is an absolutely protected writing under CCP 2018.030(a), as National Steel's first step would suggest, or work product waived by disclosure to a witness, as DeLuca's reasoning would suggest. Do not build a practice on the first answer.

How it comes out

Through the exchange demand, the deposition notice, and cross-examination at trial.

The exchange. A demand under CCP 2034.210(c) can include "all discoverable reports and writings, if any, made by" a retained expert "in the course of preparing that expert's opinion," and CCP 2034.270 requires them to be produced on the exchange date. The word "discoverable" is what brings the work product analysis into the exchange.

The deposition. A retained expert whose deposition is noticed under CCP 2025.220 must produce the materials the notice calls for no later than three business days before the deposition. CCP 2034.415. A notice can call for the expert's communications with counsel. At the deposition itself, what counsel said on the phone is fair game for the same reasons the emails are.

Trial. An expert "may be fully cross-examined as to ... the matter upon which his or her opinion is based and the reasons for his or her opinion." Evid. Code 721(a). Assumptions counsel supplied are part of the basis.

The penalty for holding back. On objection by a party who has complied, the court "shall exclude" the opinion of an expert offered by a party who has unreasonably failed to produce reports and writings under section 2034.270. CCP 2034.300(c).

Writing to a testifying expert

Put logistics in writing. Put nothing in writing you would not want read to the jury.

The practical rule follows from the cases. Once an expert is going to testify, an email telling the expert what to test, what to look for, or what result would help is an exhibit waiting to happen. The cross-examination writes itself: counsel asked you to do this, and you did not do that.

So keep the written channel to scheduling, document transfer, invoices, and the materials you want the expert to consider. Send facts and documents, not conclusions. Ask for the expert's opinion rather than proposing one, and do not send draft opinion language.

Taking the substance to a call is common practice, and it has a real benefit: there is no document to produce under CCP 2034.270 or a deposition notice. It is not a privilege. The expert can be asked what counsel said on the call, and DeLuca treats what was said as disclosed. 217 Cal.App.4th at 692. Have the conversation as if it will be described under oath, because it may be.

If you need candid strategic advice from someone technical, the cases point to the answer: a separate consultant who is never designated. Counsel can keep work product conveyed to a consultant protected "by the simple expedient of not designating the expert as a testifying expert." DeLuca, 217 Cal.App.4th at 692.

Withdrawing a designation

Possible, before the expert is deposed or the opinion is out, and only for your own tactical reasons.

A party "may, indeed, enjoy the right to withdraw an expert witness at any time prior to disclosure of that witness' proposed testimony." Williamson, 21 Cal.3d at 835. In County of Los Angeles, a defendant withdrew a designated expert who had not been deposed and kept him as a consultant; the court held the withdrawal proper, the expert's report work product, and the plaintiff unable to depose or designate him. 222 Cal.App.3d at 650, 655-656. In Williamson, by contrast, a withdrawal bought with an indemnity agreement from a codefendant did not restore anything. 21 Cal.3d at 835-836.

Once the expert has been deposed or the opinion disclosed, withdrawal comes too late.

The local layer

Everything on this page is statewide: the Civil Discovery Act, the Evidence Code, and published appellate decisions. The San Diego, Riverside and San Bernardino local rules were not checked for expert discovery provisions on this review. A case management order can set its own terms for expert discovery, so read yours.