The confession of a criminal defendant serves as a prosecutor's most compelling piece of evidence during trial. Courts must preserve a defendant's constitutional right to a fair trial while upholding the judicial interests of presenting competent and reliable evidence to the jury. When a defendant seeks to challenge the validity of that confession through expert testimony, the prosecution often contests the admissibility of the expert's opinion. Depending on the content and methodology of the expert's opinion, testimony addressing the phenomenon of false confessions may or may not be admissible. This article outlines the scientific and epistemological bases of expert testimony on false confession, notes the obstacles facing its admissibility, and provides guidance to the expert in formulating opinions that will reach the judge or jury. We review the 2006 New Jersey Superior Court decision in State of New Jersey v. George King to illustrate what is involved in the admissibility of false-confession testimony and use the case as a starting point in developing a best-practice approach to working in this area.