This chapter introduces the concept of serial murder and provides the definition of “serial killer” used by many academics. The author discusses the coining of the term “serial killer” by Robert Ressler as well as the strengths and weaknesses of the most recent information that the US Federal Bureau of Investigation (FBI) provides to the public about serial murder. Although the FBI’s current information was assembled by a highly reputable team, it paints a broad-strokes portrait of serial murder as sexually motivated and does not acknowledge or make known the stark difference between female serial killers (FSKs) and male serial killers (MSKs) in crimes and victims. This can be to the detriment of law enforcement investigations. Harrison describes how FSKs tend to be unknown or ignored, perhaps because, as author Patricia Pearson argued, people are reluctant to believe women can be murderers. Furthermore, because psychopathy is a concept frequently emerging in serial killer psychology, the author provides a primer. Case studies of FSKs Kristen Gilbert, Patty Cannon, Aileen Wuornos, and Sharon Kinne illustrate various serial killer modus operandi and psychological concepts.