1. Two Different Disclosure Tracks
Federal Rule of Civil Procedure 26(a)(2) splits expert witnesses into two categories with different disclosure obligations, and mixing them up is a common, avoidable mistake.
A retained or specially employed expert — the typical case for a paid expert witness — falls under Rule 26(a)(2)(B) and must produce a full written report, signed by the witness. A non-retained expert — most often a treating physician or another witness whose opinion arises from their own involvement in the underlying facts rather than from being hired for the case — falls under the lighter Rule 26(a)(2)(C), which requires only a disclosure stating the subject matter of the expected testimony and a summary of the facts and opinions involved. Treating an expert who should be in the first category as if they only need the second category's lighter disclosure is a fast way to have that testimony excluded.
2. What the Written Report Must Contain — Rule 26(a)(2)(B)
For a retained expert, the rule enumerates the report's required contents directly. It must include:
- A complete statement of all opinions the witness will express, and the basis and reasons for them
- The facts or data considered by the witness in forming those opinions
- Any exhibits that will be used to summarize or support the opinions
- The witness's qualifications, including a list of all publications authored in the previous 10 years
- A list of all other cases in which, during the previous 4 years, the witness testified as an expert at trial or by deposition
- A statement of the compensation to be paid for the study and testimony in the case
The 4-year prior-testimony list catches experts who don't keep a running record of their own case history — it has to be produced on demand, not reconstructed from memory under deadline pressure. Ask any expert you're vetting whether they maintain this list as they go.
3. Timing
Absent a court order or stipulation otherwise, disclosures under Rule 26(a)(2) are due at least 90 days before the trial date or the date the case is set for trial. If the disclosure is solely to contradict or rebut evidence identified by another party's expert disclosure, the deadline shortens to within 30 days after that other party's disclosure.
In practice, most federal cases run on a scheduling order that sets its own, case-specific expert disclosure deadlines — those supersede the rule's default dates. The 90/30-day figures matter mainly as the fallback when no scheduling order addresses it, and as a baseline for how much lead time a retained expert realistically needs to produce a complete Rule 26(a)(2)(B) report.
4. A Short Prep Checklist for Retaining Counsel
- Confirm which track applies — retained (full report) or non-retained (summary disclosure) — before the deadline, not at it.
- Get the compensation arrangement in writing early; it has to go in the report regardless.
- Ask the expert for their own 4-year prior-testimony list and 10-year publication list at engagement, not at report deadline.
- Check the case's actual scheduling order for its expert-disclosure date — don't assume the rule's default 90-day figure applies.
Sources
- Federal Rule of Civil Procedure 26 (Cornell LII)
- Federal Rule of Evidence 702 (Cornell LII)
- Sidley Austin — 2023 Amendment to FRE 702