Instruct earlier than the disclosure deadline implies. The binding step is conflicts screening, not availability: an expert who clears on paper can fail on a single prior engagement, and each failed candidate resets the clock.
When should counsel instruct an expert?
Early enough to absorb at least two screening cycles. Counsel routinely plan backward from the disclosure deadline using the expert's availability as the constraint, which is the wrong variable — availability is rarely what fails.
What fails is conflicts. A candidate who looks ideal on paper turns out to have advised a party's subsidiary four years ago, and the search restarts. Planning for one cycle assumes the first name works — and that one person can serve as both consulting and testifying expert, which is rarely true.
- 01
Define the opinion
Write the question the expert is being asked to answer, and what they are not being asked.
- 02
Screen first
Run conflicts against every party and counsel before any name reaches the instructing team.
- 03
Test under challenge
Put the candidate through the argument they will face, not only the one you want made.
- 04
Instruct in writing
Give the question, the documents and the limits of the opinion, on paper.
What does conflicts screening actually take?
Checking prior engagements, employment history, publications and any financial interest against every party and counsel in the matter. Done properly it happens before any name reaches counsel, so that a rejected candidate is never a disclosed one — a stricter standard than a commercial expert call ever requires.
The sequencing matters more than the thoroughness. A conflict discovered after counsel has seen a name is awkward; a conflict discovered after instruction is expensive and occasionally disclosable.
What does a late appointment cost?
The ability to reject. Late instruction means the first technically qualified candidate becomes the only candidate, and the question shifts from whether they are the right expert to whether they will do.
That is how experts who cannot survive cross-examination end up instructed. Technical qualification and the ability to hold an opinion under challenge are different attributes, and testing for the second takes time nobody has left. Putting a candidate in front of peers is one way to test it early.
| Instructed early | Instructed late | |
|---|---|---|
| Candidates available | Several, each screened before being seen | Whoever clears first |
| Screening | Two or more cycles absorbed | One cycle, with no room to fail |
| Selection question | Which expert is strongest under challenge | Whether this expert will do |
What if the expert must change?
It is possible and it is visible. Disclosure rules in most jurisdictions mean opposing counsel will see that an expert has changed and will ask why, and the answer is rarely helpful.
The cost of changing almost always exceeds the cost of screening properly at the start, which is the practical argument for building the extra cycle into the timetable rather than hoping it is not needed.
How should counsel brief an expert?
In writing, with the question, the documents relied on, and the limits of the opinion sought. An expert briefed verbally produces an opinion that shifts under challenge, because they are reconstructing the scope from memory while being cross-examined on it. A written brief does for litigation what a fixed discussion guide does for commercial research.
Stating the limits explicitly is the part most often skipped and the part that protects the opinion. An expert who has been told what they are not being asked can decline to speculate without appearing evasive.