California Code of Civil Procedure section 2034 sets the rules for how parties in a civil lawsuit disclose their expert witnesses to each other before trial. Once a trial date is set, any party can demand a simultaneous exchange of expert information, and every side must then hand over expert lists, sworn declarations, and reports on the same day. Miss a deadline or skip a required piece, and the court can bar your expert from testifying.
How the Exchange Starts
The process begins when a party serves a written demand for exchange of expert witness information. The demand must identify the party making it and state that it is made under CCP 2034.1California Legislative Information. California Code of Civil Procedure 2034.230 – Demand for Exchange of Expert Witness Information
The demand can request up to three categories of information:2California Legislative Information. California Code of Civil Procedure 2034.210 – Demand for Exchange of Expert Witness Information
- The names and addresses of every person the party expects to present as an expert at trial.
- Signed declarations covering retained experts, party employees, and parties themselves when offering expert opinions.
- All discoverable reports and writings the retained expert prepared while forming opinions for the case.
Most demands ask for all three. Because the exchange is simultaneous, neither party gets to tailor its expert strategy to what the other side revealed first.
The Deadlines You Cannot Miss
Two dates matter, and they interact.
The demand must be served no later than the 10th day after the initial trial date is set, or 70 days before that trial date, whichever is closer to trial.3California Legislative Information. California Code CCP 2034.220 – Demand for Exchange of Expert Witness Information Serve it late and you may have waived the right to compel expert disclosures.
The demand itself sets the exchange date. That date must be either 50 days before the initial trial date or 20 days after service of the demand, whichever is closer to trial.1California Legislative Information. California Code of Civil Procedure 2034.230 – Demand for Exchange of Expert Witness Information If it lands on a weekend or court holiday, the exchange moves to the next court day closer to trial. On a showing of good cause, a court can order an earlier or later date.
The practical effect: the exchange usually happens about seven weeks before trial. Both sides deliver their materials on the same day, either at an in-person meeting of counsel or through any authorized method of service.
What the Expert Witness Declaration Must Contain
For retained experts, party employees offering expert opinions, and parties themselves offering expert opinions, a list of names is not enough. Counsel for the disclosing party must sign a declaration under penalty of perjury that includes each of the following:4California Legislative Information. California Code CCP 2034.260 – Exchange of Expert Witness Information
- A brief narrative of the expert’s qualifications.
- A brief narrative of the general substance of the testimony the expert is expected to give.
- A representation that the expert has agreed to testify at trial.
- A representation that the expert will be sufficiently familiar with the case to give a meaningful deposition.
- The expert’s hourly and daily rates for deposition testimony and for consulting with the retaining attorney.
Omitting any of these items opens the door to a motion excluding the expert.
Non-retained experts who are not party employees and were not hired to form opinions for the case get lighter treatment. The party only lists the name and address. No declaration, no report production. Their trial testimony is generally limited to opinions formed through their own firsthand experience rather than case-specific preparation.
Producing Reports and Writings
When the demand includes reports, each party must produce every discoverable report and writing the retained expert prepared while forming opinions for the case.5California Legislative Information. California Code of Civil Procedure 2034.270 Production happens on the same date as the list exchange. Reports, analyses, and written summaries that shaped the expert’s conclusions all fall within the scope.
Failing to produce these materials is independently sanctionable. A court can exclude the expert’s testimony for the failure to hand over reports even if the party properly listed the expert and submitted a declaration.6California Legislative Information. California Code of Civil Procedure 2034.300
Deposing the Other Side’s Experts
Once a party receives the exchange list, it can depose anyone on it. Standard California deposition rules apply, with a few features specific to experts.7California.Public.Law. Code of Civil Procedure Section 2034.410
Who Pays the Fee
The party noticing the deposition pays the expert’s reasonable and customary hourly or daily rate. The clock runs from the time noticed in the subpoena, or from the expert’s arrival if the expert is late, until the expert is dismissed. If opposing counsel arrives late, that attorney personally pays for the delay, but the rate charged cannot exceed what the retaining party pays.8California Legislative Information. California Code CCP 2034.430 – Expert Witness Deposition Fee
A daily fee may only be charged when the expert actually attends for a full day, or when the deposing party required the expert to reserve the entire day. That rule prevents a full-day charge for a two-hour deposition.
Tendering the Fee
The deposition notice alone does not compel the expert to appear. It must be accompanied by a tender of the expert’s fee. Without the tender, the expert has no obligation to show up.9California Legislative Information. California Code of Civil Procedure CCP 2034.460
Fee Disputes
If the parties disagree about whether the rate is reasonable, either side can move to set the fee. The losing party on that motion faces mandatory monetary sanctions unless the court finds the position was substantially justified.10California Legislative Information. California Code of Civil Procedure 2034.470
What Happens If You Don’t Comply
The main penalty for breaking the disclosure rules is exclusion of the expert’s testimony at trial. If a party that fully and timely complied with its own obligations objects, the court must exclude expert opinion from a party that unreasonably failed to do any of the following:
- List the expert on the exchange.
- Submit the required declaration.
- Produce the expert’s reports and writings.
- Make the expert available for deposition.
CCP 2034.300 uses “shall,” which makes exclusion mandatory once those elements are established, not discretionary.6California Legislative Information. California Code of Civil Procedure 2034.300 In cases where expert testimony carries the claim or the defense, exclusion can end the case.
When an Undisclosed Expert Can Still Testify
CCP 2034.310 identifies two exceptions.11California Legislative Information. California Code of Civil Procedure CCP 2034.310
First, if another party listed the expert and that expert was subsequently deposed, any party can call the expert at trial, including one that never designated the expert.
Second, a party can call an unlisted expert solely to impeach an opposing expert. The impeachment witness can challenge the factual foundations the other expert relied on, but cannot simply offer a competing opinion on the same issue. The line runs between attacking the foundation of an opinion and contradicting the opinion itself.
Adding or Amending Experts After the Deadline
Missing the initial exchange does not always close the door. Under CCP 2034.610, a party that participated in the timely exchange can move for permission to add a new expert or to change the expected testimony of a listed one.12California Legislative Information. California Code of Civil Procedure CCP 2034.610 The motion must be filed early enough that the opposing side can still depose the new or amended expert before the discovery cutoff. In exceptional circumstances the court may allow a later filing.
Courts do not grant these motions freely. Before approving one, the judge must find that the opposing party will not be prejudiced on the merits, and either that the moving party could not have identified the expert earlier despite acting with reasonable diligence, or that the failure resulted from mistake, inadvertence, surprise, or excusable neglect.13Justia. California Code of Civil Procedure 2034.620 – Conditions for Granting Motion A party relying on excusable neglect must also show it acted promptly once it decided to add the expert and served the required information without delay.
Even when the court grants the motion, it usually attaches conditions: the new expert must be made immediately available for deposition, the opposing side may designate additional experts in response, and the trial date may be continued. The court can award costs and litigation expenses to the party that opposed the motion, and the losing side faces mandatory monetary sanctions unless the court finds substantial justification or other circumstances making sanctions unjust.
Compliance Is Not the Whole Battle
Clearing the CCP 2034 disclosure hurdles does not guarantee the expert will testify. California trial courts serve as gatekeepers over admissibility under the California Supreme Court’s decision in Sargon Enterprises, Inc. v. University of Southern California, and can exclude expert opinion that rests on unreliable data, reasoning unsupported by the underlying material, or speculation.14Stanford Law School. Sargon v. Univ. Southern Cal. The court examines the methodology and whether there is too large a gap between the data and the opinion. It does not weigh competing experts against each other or substitute its own judgment for the expert’s conclusions. An expert who fully complies with the disclosure rules can still be excluded at trial if the opposing party successfully challenges the reliability of the opinions under Sargon.