An exert witness is not a witness in the normal sense. While a witness is someone who has first-hand knowledge of a certain crime or dramatic event, an expert witness has no first-hand knowledge. Rather, his witness is sought to clarify, corroborate, buttress, negate, deny, analyze or comment on a certain issue about which expert opinion is considered critical to the resolution of a dispute.

An expert witness is a witness, who by virtue of education, profession or experience, is believed to have special knowledge of his subject beyond that of the average person, sufficient that others may officially (and legally) rely upon his opinion. Experts may be called upon to opinionate on a certain issue, like the serverity of an injury, the cause and mode of death, degree of insanity, etc. As law becomes increasingly more technical, the judges find it mandatory to call upon the expert opinion of others in areas in which they themselves have no expertise on. Thus expert opinion is a contrivance to raise the ambit of knowledge based upon which an objective and considered decision may be offered. The expert opinion may be sought by both parties, may be cross examined, and all the data as well as evidence utlized for arriving at the opinion becomes open for examination by both parties. At times both parties bring their own experts offering diverging opinions. In penal cases, the responsibility of the expert becomes very great as the decision of the judge or jury hinges upon his or her opinion, and the expert may be liable to heavy punishment in case of fraudulent opinions.

The earliest known use of the expert opinion came in English law in 1782 when the opinion of engineer John Smeaton was sought regarding a case of desilting of Wells harbour in Norfolk. Today, expert witnesses are sought around the world in all sorts of cases, and they are of immense help in the distribution of justice.

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