The interest of justice is best served only when the witness produces unbiased testimony. In the litigation process, witnesses and their testimonies play a pivotal role. A witness helps to cross-examine the shreds of evidence presented in the case and adds a new dimension to the case by providing additional insights to the litigation.
A witness who possesses knowledge, skill, experience, training, or education which helps the trier of the fact to understand the evidence or determine a fact in issue, is called an Expert Witness. There are certain guidelines to be strictly followed by the parties for using an expert witness in their litigation.
Prior information or Disclosure
Under Federal Rule of Evidence 702; 703 and 705, a party who is using an expert witness must disclose theidentity of the expert witness in advance.The expert witness must provide itswritten report containing a complete statement, facts, and data, proposed exhibits, qualifications of the past 10 years along with the list of publications, statement of compensation, history of testified cases of past 4 years.
However, if the party fails to disclose the identity of the expert witness, or could not provide the necessary information, then the party is refrained from using those facts and information or the expert witness in the litigation until adjudged harmless or justified.
Type of expert witnesses
While the expert witnesses are required to provide written reports, some are often excluded from this provision. These witnesses are the non-retained or employee witnesses. They have to present a summary of their facts and opinions along with the subject matter.In such cases, the conversations between the lawyer and witness are non-discoverable to the employer, if he/ she/ they are also related to the case.
Limits of Trial preparation of the expert
Any draft, written/ oral/ electronic or otherwise, along with supplements are duly protected by Rules 26(b)(3)
and 
5 of the Federal rules of Civil Procedure.The party’s lawyer and the expert witness can communicate through any means, which is protected. The exclusions are compensation for expert’s study, facts or data provided by the lawyer and assumptions.Other communications with anyone, apart from the lawyer, are discoverable and they can be cross-questioned about possible alternatives ways of the studies.
A party may not be able to acquire facts and opinions held by the expert beforehand. They may explicitly do so under exceptional situations in which the other party fails to obtain facts and opinions by any other means. For example, in North Carolina, expert disclosures can only be obtained through interrogatories, while in New York, interrogatories of experts are permitted only in special circumstances.
