A witness who qualifies as an expert because of knowledge, skill, experience, training, or education may testify as an expert if scientific, technical, or other specialized knowledge will assist the judge, jury, or other factfinder to understand the evidence or determine a contested fact issue.

But there is no rigid formula for determining whether a particular witness is qualified to testify as an expert. Generally there must be a fit between the subject matter at issue and the expert witness’s familiarity with the subject matter. And this determination is made by the judge, who acts as a gatekeeper to only allow reliable expert witness testimony to be heard and considered by the judge or jury—and to exclude such testimony when it is not reliable.

In Vermont, as in many jurisdictions, the admissibility of expert witness testimony is governed by rules that are designed to ensure that any expert evidence presented is both relevant and reliable. An individual may qualify as an expert witness based on their knowledge, skill, experience, training, or education, and they may testify if their specialized knowledge will help the court understand the evidence or determine a fact in question. The determination of whether a witness is qualified as an expert is not based on a strict formula but rather on whether there is an appropriate fit between the witness's expertise and the subject matter of the case. The judge serves as a gatekeeper, with the responsibility to admit expert testimony that is reliable and to exclude it when it is not. This gatekeeping function is crucial to ensuring that the evidence presented is of a standard that can be considered credible and authoritative by the judge or jury.