In a perfect world, an expert’s testimony wouldn’t change just because the courtroom does. But those who work in complex litigation know the reality: state rules can dramatically alter what experts must disclose before trial and what they’re allowed to say during it.
While federal court offers a familiar playbook, the guidance can shift—sometimes subtly, sometimes drastically—regarding what’s permissible in certain state courts. These differences affect everything from how teams collaborate with experts to how tightly testimony on the stand must track disclosures. And as matters increasingly span multiple jurisdictions, understanding these variations isn’t just procedural awareness; it’s a strategic advantage. Let’s examine the spectrum of these guidelines and how they shift by location.
Federal Court: The Structured Baseline
F.R.C.P. Rule 26 sets out a clear, structured reporting framework that establishes the disclosures experts must make and the information opposing counsel is entitled to receive.
Just as important, federal rules protect draft reports and most attorney–expert communications. Counsel can refine narratives, test alternative formulations, and prepare the expert with confidence that drafts and emails won’t become discovery fodder.
At trial, courts often apply a strict “stick to what’s in the report” approach. Opinions not disclosed or not clearly supported by the bases in the report risk exclusion under F.R.C.P. Rule 37. The emphasis is on predictability and preventing surprise.
California: Broad Discovery and Strict Boundaries
California offers a very different environment. Its expert discovery process, well-known as the 2034 exchange, requires parties to produce:
- Expert identities
- Detailed declarations on subject matter and substance
- Fee information
- All discoverable “reports and writings” related to the expert’s work
This final requirement is where California diverges sharply from federal court.
Draft reports, notes, outlines, spreadsheets, and sometimes communications that might be protected elsewhere may become discoverable in California. Practitioners must become more cautious because of the rules outlined above, and teams must assume that written commentary could be reviewed by opposing counsel.
California trial courts also enforce disclosure requirements aggressively. If an opinion wasn’t included in the exchanged materials or explored in deposition, it may not come in at trial. The system is built around eliminating surprise, and judges are quick to limit testimony that strays beyond what was disclosed.
New York: Narrative Disclosures and Judicial Discretion
New York takes yet another approach. Under CPLR 3101(d), parties provide narrative expert disclosures rather than formal reports. These disclosures must provide reasonable detail across the following:
- Subject matter
- Facts and opinions
- Grounds for those opinions
- Qualifications
There is no required format, and practices can vary not just by county, but by courtroom.
Because New York lacks the “four corners of the report” constraint (which in other jurisdictions limits an expert’s trial testimony strictly to what appears within the four corners of their written report) judicial discretion plays a central role. Without a formal report for the court to police, New York judges may allow an expert to expand beyond the disclosure if the testimony is a logical extension of the opinions provided and does not create unfair surprise. At the same time, they may preclude testimony entirely if a disclosure is too thin, too vague, or served too late.
The result is a system defined less by rigid structure and more by fairness and practicality, despite unpredictability being a part of the equation.
Texas: A Move Toward the Federal Model
Texas updated its rules in 2021, aligning more closely with federal practice. Retained testifying experts now face disclosure requirements similar to F.R.C.P. 26, including detailed descriptions of opinions and bases.
Notably, Texas adopted federal-style work-product protections for draft reports and most communications with counsel, giving teams more freedom to collaborate during preparation.
At trial, testimony typically must stay within the disclosed opinions, though courts may show slightly more flexibility than their federal counterparts. The practical takeaway: Texas feels familiar to federal practitioners, but the nuances still matter.
Why These Differences Matter
- Collaboration Looks Different in Each State: In federal court or Texas, draft-heavy collaboration is safe. In California, those drafts could be produced. In New York, there may be no drafts at all—because there’s no report requirement.
- Disclosure Drives Trial Strategy: Some jurisdictions treat expert disclosures as binding roadmaps; others treat them as guideposts. This changes how tightly counsel guides testimony and how early teams must finalize their positions.
- Privilege and Work Product Aren’t Universal: Counsel accustomed to federal protections may inadvertently generate discoverable material in states with broader rules. Knowing the discoverability landscape early protects both strategy and narrative.
- Multi-Jurisdictional Matters Require Tailored Playbooks: When matters cross jurisdictions with divergent disclosure rules—whether federal, state, or a mix—uniform expert-preparation models rarely hold. Teams must adopt venue-specific protocols for drafting, disclosure, and deposition preparation.
Practical Implications for Litigation Teams – Key Points to Keep in Mind
1. Disclosure rules shape the entire expert workflow.
The differences among federal, California, New York, and Texas regimes determine when expert work begins, how much must be disclosed, and how tightly teams must lock in opinions.
2. Documentation carries different strategic risks by venue.
Federal courts and Texas protect drafts and communications; California exposes them; New York often bypasses written reports altogether. These contrasts make documentation practices outcome-relevant.
3. Testimony flexibility varies across jurisdictions.
Federal and California courts enforce strict adherence to disclosed opinions, while New York allows more expansion—though thin disclosures risk preclusion. Texas largely follows federal expectations.
4. Communication practices must match discovery exposure.
The degree to which drafts, notes, and attorney–expert exchanges are discoverable directly influences how teams collaborate and prepare experts.
5. Multi-state matters magnify these differences.
When cases span jurisdictions, varying disclosure obligations reshape timelines, risk, and even expert selection. A single preparation model rarely fits all forums.
How Experts Can Assist in Complex Litigation
Experts are central to modern litigation, but the rules governing their disclosures and testimony vary dramatically across jurisdictions. Federal court offers structure and protection; California demands transparency and rigorous adherence; New York relies on narrative and discretion; Texas blends federal-style protections with its own procedural expectations. By approaching expert preparation with an awareness of these jurisdictional nuances, legal teams can work more confidently with DOAR’s consultants to ensure experts are positioned to communicate clearly and effectively at trial.