Introduction
How or why some scientific evidence or expert witnesses are allowed to be presented in court and some are not can be confusing to the casual observer or a layperson. However, there is significant precedent that guides how these decisions are made. Our discussion here will briefly outline the three major sources that currently guide evidence and testimony admissibility: the Frye Standard, the Federal Rules of Evidence, Rule 702; and, the Daubert Standard, as well as who can serve as an expert witness in a court of law.