Two experts can review the same file, walk the same site and form similar opinions, then end up in very different positions once a case moves toward litigation. The difference isn't the work itself. It's whether the expert was retained to testify or retained only to consult, a decision that determines what opposing counsel can discover about the engagement.
Federal Rule of Civil Procedure 26(b)(4) draws the line. A testifying expert, one expected to offer opinions at trial, must disclose a written report stating every opinion and the basis for it and is subject to deposition on that basis. A consulting expert retained only to help prepare for litigation, without an expectation of testifying, is treated very differently: their facts and opinions are generally shielded from discovery entirely, except in exceptional circumstances, most often when the same information can't be obtained any other way.
- 1. Draft reports carry real, but not unlimited, protection. Rule 26(b)(4)(B) protects drafts of a testifying expert's report from discovery. It does not protect the underlying facts and data the expert actually considered in forming an opinion; those remain discoverable regardless of draft status.
- 2. Attorney-expert communications are protected, with named exceptions. Rule 26(b)(4)(C) shields most communications between counsel and a testifying expert, but carves out three categories: compensation terms, facts or data counsel provided that the expert considered and assumptions counsel provided that the expert relied on.
- 3. A consulting expert's opinions are generally off-limits entirely. Under Rule 26(b)(4)(D), a non-testifying consulting expert's facts and opinions can only be discovered on a showing of exceptional circumstances, typically that the opposing party has no other practical way to obtain equivalent information, evidence that's since been altered or destroyed, for example.
- 4. Switching an expert's role can waive the protection retroactively. Moving a consulting expert into a testifying role at any point in the case generally exposes that expert's prior work to the same discovery a testifying expert faces from the start. The decision isn't easily reversible once the switch is made.
- 5. State courts don't automatically follow the federal rule. Many states have adopted rules that closely mirror FRCP 26(b)(4), but not all of them. The details (what "exceptional circumstances" requires, how communications are treated) vary by jurisdiction. Confirm the actual rule in the forum before assuming federal protections apply.
For attorneys and carriers, the practical takeaway is to decide an expert's role deliberately at retention and document it in the engagement letter rather than leaving it implicit. Keep communications with a consulting expert as disciplined as if they might later testify, since a change in strategy can turn a consulting engagement into a testifying one faster than expected. And don't assume protection is automatic: it's a legal standard with real exceptions, not a blanket shield.
This article is a general informational overview, not legal advice and does not create an attorney-client or expert-client relationship.
