The prevalence of serial murder is low; however, it has been the focus of much academic and popular attention. Despite a considerable research base on serial murder, there is still debate as to how it should be defined. This article examines often used definitions of serial murder, followed by a critique of some of the main components of these definitions. From this, a definition is advanced with rationales for the inclusion of the characteristics in the proposed definition. This analysis provides for some clarity in the identification of serial murder and those aspects of the crime used to define it.