Expert Witness Definition

A person who's qualified, by reason of education, training, or experience, to provide expert opinions that will assist the trier of fact—the jury or, in a bench trial, the judge—in reaching conclusions. In a court case, the judge acts as a "gatekeeper," deciding whether an expert's testimony is sufficiently reliable and relevant to allow it during trial. Judges do this by examining several factors identified in Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993). See also Kumho Tire Co., Ltd. v. Carmichael, 526 U.S. 137 (1999).

Scientific, medical, and other experts, who typically are paid for their work, can be critical in many kinds of disputes, including personal injury, product liability, medical malpractice, and criminal cases. Quite often, these cases end up being a "battle of the experts." Expert witness fees can easily run into the thousands or tens of thousands of dollars, depending on the complexity of the case and the issues.