This chapter explores the multifaceted typologies within serial killer research, highlighting the complex interplay of characteristics that often overlap among distinct categories. By examining various frameworks developed throughout the field, this chapter reviews how scholars have categorized serial killers based on psychological, behavioral, and contextual factors. Several cornerstone typologies are reviewed, including the organized/disorganized typologies and geographic typologies. Additionally, more recent typologies for specific populations of serial killers are discussed. The discussion emphasizes the need for a nuanced understanding of serial killers, arguing that rigid classifications may not adequately capture the intricacies of individual cases. The present chapter provides a comprehensive overview of the prevailing typologies and the discourse on how criminologists and forensic psychologists conceptualize the serial homicide offender.