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 Alabama, the admissibility of expert witness testimony is governed by both state statutes and case law, which align with the principles of the Federal Rules of Evidence. An individual may testify as an expert if they have specialized knowledge, skill, experience, training, or education that is relevant to the case and can help the court understand the evidence or a fact in issue. However, there is no strict formula for determining who qualifies as an expert; the key is that there must be an appropriate connection between the expert's expertise and the subject matter of the dispute. The trial judge serves as a gatekeeper, tasked with ensuring that the expert testimony is not only relevant but also reliable before it is presented to a jury or considered by the court. This gatekeeping function involves assessing the methodology and principles that underpin the expert's opinion, ensuring that the testimony is based on sufficient facts or data and is the product of reliable principles and methods that have been properly applied to the facts of the case. This standard is derived from the landmark case Daubert v. Merrell Dow Pharmaceuticals, Inc., which is applied in federal courts and many state courts, including Alabama, to evaluate the admissibility of expert testimony.