A consulting expert helps counsel understand a technical position and is generally protected as work product. A testifying expert states an opinion on the record, and their basis, materials and prior positions become disclosable. The distinction decides what you can safely ask.
What is a consulting expert?
An expert instructed to help counsel understand the technical position, without giving evidence — closer to an embedded adviser than to a witness. Their work is generally protected in most jurisdictions, which is what allows counsel to explore a theory that may not hold without disclosing that they explored it.
That protection is the reason the role exists. Testing a weak argument is a normal and necessary part of preparing a case, and it becomes much harder to do if every avenue examined is later visible to the other side.
| Consulting expert | Testifying expert | |
|---|---|---|
| Role | Helps counsel understand the technical position | States an opinion on the record |
| Discoverability | Generally protected as work product | Opinion, basis and materials are disclosed |
| Selected for | Breadth and candor | Ability to hold an opinion under cross-examination |
What does a testifying expert do?
States an opinion on the record and defends it. Their materials, working assumptions, instructions and often their prior published positions become disclosable, and everything they considered is fair ground for cross-examination.
That changes what they should be asked. A testifying expert exploring an argument speculatively is generating disclosable material about a position their own side may abandon. Where that exploration belongs is the same question as whether to embed an adviser or scope a discrete project.
Which one is discoverable?
Generally the testifying expert, and generally not the consulting one — but the protection is not absolute and the rules vary materially between jurisdictions. This is a point to check locally rather than to assume from a summary.
What is consistent across systems is the direction: giving evidence exposes the basis for it, and not giving evidence does not.
Jurisdiction is also worth establishing at the point of instruction rather than when a dispute arises. Cross-border matters can put the two experts under different rules, and an arrangement that protects the consulting work in one forum may not in another — a question for local counsel before the instruction rather than after it.
Can one person be both?
They can, and it usually costs you the protection. Once someone becomes a testifying expert, work they did while consulting is much harder to keep out of disclosure, and the argument that it should be excluded is one you have to win rather than assume.
Where a matter needs both functions, instructing two people is the cleaner structure and often the cheaper one once the disclosure fight is priced in — the same calculation a corporate development team makes on a disputed earn-out.
Which does your matter need?
Usually both, sequentially. A consulting expert to establish whether the technical argument holds at all, then a testifying expert selected for the narrower opinion that survived that test — which is why the instruction date has to absorb two screening cycles.
Running it in the other order — instructing a testifying expert and asking them to explore — is how cases end up disclosing the weaknesses they were investigating.
Sequencing them also has a budget consequence worth planning for. The consulting stage is where most of the technical exploration happens and where the hours accumulate, and the testifying instruction that follows is narrower and shorter because the ground has already been cleared. Matters that instruct a testifying expert first tend to spend more in total, because the exploration happens at testifying rates and generates disclosable material while it does.