Determining the scope of recourse to expert opinion in crimes resulting in bodily harm is of particular importance, as the complexity of such crimes makes expert involvement essential for uncovering the truth. This article examines the scope and legal basis of referring to experts from the perspectives of Islamic jurisprudence and the Iranian Islamic Penal Code. The research adopts a descriptive, analytical, and comparative methodology. The findings indicate that Islamic jurists, and consequently the Iranian legislator, require judges to rely on expert opinions in identifying external manifestations of various legal subjects, including the loss of bodily faculties (such as smell, taste, hearing, sight, speech, and intellect), the classification of injuries, the determination of the transmissibility or non‑transmissibility of injuries, and the distinction between principal and accessory organs. Moreover, in determining diyah (blood money) and arsh (compensatory damages for unquantified injuries), consultation with experts is deemed indispensable. According to the preferred doctrinal view, the judge is responsible for determining attribution and causation; however, depending on the nature of the issue, recourse should be made either to custom (ʿurf) in non‑technical matters or to expert opinion in technical and specialized matters. While the identification of customary concepts falls within the authority of prevailing custom, the interpretation of religious and jurisprudential concepts necessitates reference to qualified specialists in this field, namely Islamic jurists.