Criminal negligence is a degree of the mental element of a crime. Given its importance, clarifying its characteristics is essential. The unintentional nature of a crime does not eliminate the need for a mental element; as such crimes require specific mental processes and behavioral traits. Although negligence, as part of the mental element, is secondary to criminal intent, their shared aspects necessitate a comprehensive and precise definition of negligence to clarify its conceptual components and criteria. This approach helps delineate the ambiguous boundaries and overlaps between negligence and other criminal law concepts, as well as its implications for criminal responses. Using a descriptive-analytical method, this study addresses: What are the conceptual components of criminal negligence, and in which crimes is it recognized? Findings indicate that the voluntary commission of unconventional behavior foreseeably leading to an unjustifiable criminal outcome, without requiring intent in preparatory stages and with an established causal relationship, constitutes criminal negligence. The Islamic Penal Code of 2013 demonstrates that negligence-based crimes have expanded in Iran’s criminal legislation, encompassing concepts like unintentional causation in homicide, medical liability, liability from another’s conduct, bankruptcy, and certain crimes against judicial justice, all shaped around criminal negligence.