California Expert Witness Rules: What Litigators Need to Know

California expert witness rules are detailed and nuanced, requiring strict compliance to ensure admissibility and preserve a party’s right to present expert testimony. Failing to meet procedural requirements can result in the exclusion of crucial testimony, damaging a party’s position at trial. Attorneys must understand not only state-level standards under the California Code of Civil Procedure (CCP), but also how local rules and case law interact with expert witness designations, disclosures, and evidentiary challenges.

Designation Requirements

California adheres to a bifurcated discovery system, requiring parties to formally designate their expert witnesses after the initial exchange of factual discovery. Under CCP 2034.210, each party intending to offer expert testimony must serve a designation identifying the experts they plan to call at trial. This includes:

• The name and address of the expert
• A brief narrative statement of the general substance of the testimony the expert is expected to give
• A declaration regarding the expert’s qualifications if the party seeks to elicit opinion testimony

California recognizes two tiers of experts: retained experts, who are specifically hired for litigation, and non-retained experts, such as treating physicians or professionals whose testimony arises from their involvement in the events underlying the litigation. Only retained experts require detailed disclosures and may be deposed as a matter of right.

Expert Disclosure Process: CCP 2034.210

The expert witness disclosure process in California is governed primarily by CCP §§ 2034.210–2034.310. Disclosures occur after the trial has been set and must follow the statutory timeline:

• The initial exchange of expert information must be served 50 days before trial or 20 days after the service of a trial date, whichever is closer to the trial date (CCP § 2034.230).
• Parties then have 20 days after the initial exchange to submit a supplemental exchange, limited to experts rebutting matters disclosed by the opposing party (CCP § 2034.280).

Expert witness declarations must accompany any designation of a retained expert and must include a statement that the expert is available to be deposed and will testify at trial. Without this declaration, the expert designation may be deemed invalid.

Required Declarations

Declarations are mandatory for retained experts and must meet the requirements outlined in CCP § 2034.260(c). Each declaration must affirm that:

1. The expert has agreed to testify at trial,
2. The expert is sufficiently qualified to provide the opinions stated, and
3. The party will produce the expert for deposition.

Courts take a strict approach to these requirements. In Bonds v. Roy, 20 Cal. App. 4th 140 (1993), the court affirmed the exclusion of expert testimony where a party failed to provide a valid expert declaration. This case serves as a cautionary example that mere intention to call an expert is insufficient—statutory formalities must be observed.

Fees and Compensation

California allows retained experts to charge reasonable fees for time spent in deposition, trial preparation, and court testimony. Under CCP § 2034.430, the party seeking to depose an expert must tender the expert’s hourly rate before the deposition proceeds. Disputes over fees are typically resolved by the court upon motion.

It is also important to distinguish between party-retained experts and court-appointed experts under Evidence Code § 730. Court-appointed experts are compensated by the court or apportioned between the parties, as determined by the judge.

Discovery Scope and Limitations

Once designated, a retained expert is subject to deposition, and the opposing party may inquire about the expert's opinions, qualifications, and the basis for their testimony. However, limitations exist:

• Draft reports and communications between attorneys and experts are generally discoverable, unless protected by privilege.
• Under CCP § 2034.310, parties may demand production of all writings or reports made by the expert in connection with the case.
• Experts must appear for deposition upon reasonable notice, and objections must be lodged appropriately or risk being waived.

California courts often follow a narrow interpretation of discovery limitations, especially where opposing counsel seeks to uncover the foundation of an expert’s opinion. Failure to disclose critical material may result in preclusion under CCP § 2034.300.

Admissibility Standards

California’s test for expert admissibility follows the Kelly/Frye standard (now modified in part by People v. Leahy, 8 Cal.4th 587 (1994)), focusing on whether the methodology used by the expert is generally accepted in the relevant scientific community.

Unlike federal courts applying Daubert, California courts continue to apply the general acceptance standard under People v. Kelly, 17 Cal.3d 24 (1976), in criminal cases and scientific civil matters. However, in Sargon Enterprises, Inc. v. USC, 55 Cal. 4th 747 (2012), the California Supreme Court clarified that trial judges must also act as gatekeepers, excluding speculative or unreliable expert testimony even if the methodology is widely accepted.

Key Deadlines & Strategy Notes

Compliance with California’s expert disclosure deadlines is not optional. Failure to properly designate, exchange, or support experts can be fatal to a party’s claims or defenses. Strategic considerations include:

• Early retention of experts to allow adequate time for report preparation and deposition readiness,
• Careful management of supplemental designations to rebut new information presented by the opposing side,
• Ensuring all disclosures and declarations are timely, accurate, and complete.

Attorneys should also be alert to motion cut-off dates, as expert testimony can often be challenged under motions in limine or motions to exclude based on statutory noncompliance or evidentiary unreliability.

State-Specific Statutes & Local Rules

California’s statewide statutory framework is supplemented by local court rules, which may modify expert-related procedures. For example, some jurisdictions require early exchange of expert witness lists, impose shortened timelines for expert depositions, or establish local protocols for case management orders involving experts.

Attorneys practicing in Los Angeles, San Francisco, or other populous counties must consult the local rules and individual judge standing orders. Failure to follow local procedure can lead to exclusion, sanctions, or both.

Additionally, when a court appoints an expert under Evidence Code § 730, parties must follow specific procedures for objecting to the appointment, examining the court expert, and presenting rebuttal expert testimony.