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 Montana, as in many jurisdictions, the admissibility of expert witness testimony is governed by rules that require the testimony to be 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 expertise can help the court understand the evidence or determine a fact in question. However, there is no strict formula for deciding if a witness is qualified as an expert; the key is that there must be an appropriate match between the witness's expertise and the subject matter of the case. The judge serves as a gatekeeper, making the critical determination of whether the expert's testimony is sufficiently reliable to be presented to the jury. This gatekeeping role involves assessing factors such as the methodology used by the expert and whether it is scientifically valid and applicable to the facts of the case. The judge's decision to admit or exclude expert testimony can significantly impact the proceedings, as only reliable testimony will be allowed to inform the judge or jury's decisions.