An expert witness is someone who is recognized by a court as an authority on a topic who has knowledge beyond that accessible to the average person. In order to be accepted as an expert witness, the witness must generally present his or her qualifications on the stand so that the judge and jury understand what sets the witness part from other witnesses. Rather than testifying on legal matters, expert witnesses provide factual information and analysis which may be beneficial to a case.
Expert witnesses may have experience, training, skills, or education which are not common to the general public. A doctor, for example, is usually treated as an expert witness on the stand because not everyone has the benefit of a medical education and experience in practice as a doctor. Many expert witnesses provide scientific and technical information. For example, a meteorologist might provide information about a storm system which is relevant to the case, or a mechanical engineer might discuss the function and failure of a device involved in a case.
Some expert witnesses specialize in providing testimony, which is usually given after the witness has reviewed the relevant material and assembled factual information. These witnesses can be questioned by both the defense and the prosecution, and the opposing side may opt to bring in an expert witness of its own to rebut the testimony of the original witness.
Others may offer fact finding services without testifying. A defense lawyer, for example, might ask a forensic psychiatrist to examine the defendant and offer a professional opinion which may contribute to the way in which the lawyer forms the case. In these cases, the interactions between lawyer and expert witness are protected by confidentiality, but if a lawyer brings information prepared by the witness into court, that witness could potentially be called to the witness stand.
Several nations have professional associations of people who serve as expert witnesses. Members of these organizations generally present their qualifications for acceptance, and they agree to be listed in public directories which are made available to the legal community, so that lawyers can find experts in various topics. Witnesses do not need to belong to such an organization to be treated as expert witnesses.
Generally, the more qualified someone is, the more desirable he or she is as an expert witness. People working in high profile positions at organizations and institutions which set the standards in the are of expertise are generally more sought after, as are witnesses with ample publications to their names.