Serial murder is defined as “the killing of three or more people over a period of more than 30 days, with a significant cooling-off period between killings.” Researchers have identified four core elements that distinguish serial murder from other types of homicide: (1) repetition; (2) lack of a pre-existing relationship; (3) compulsion to kill; and (4) lack of an apparent motive. The characteristics of serial killers have been widely studied, with different researchers developing different categories of serial murderers. The Federal Bureau of Investigation (FBI) has divided serial murderers into two categories--organized and disorganized--while other classification systems divide serial murderers into four offender types based on their behavioral profile--the visionary killer, the mission-oriented killer, the hedonistic killer, and the power/control oriented killer. These categories are described in turn before the authors turn to a consideration of how fantasy and control provide motivation for serial killers. Theoretical explanations for serial murder are presented and include social psychological and biological perspectives. Social psychological perspectives, which include the Trauma Control Model, the Frustration-Aggression Hypothesis, and the Diathesis-Stress Model, focus on the role of individual psychological disorders and social factors, such as sexual abuse and unstable home environments. For example, the Trauma Control Model argues that serial murder is a direct result of severe childhood trauma suffered by the serial killer while the Frustration-Aggression Hypothesis contends that serial murderers kill to overcome past humiliations. Biological perspectives, on the other hand, focus on the role of individual biology and genetics, such as the identification of an extra Y chromosome and low levels of serotonin, as contributing factors to serial murder. Treatment approaches generally focus on early intervention techniques. Apprehension approaches are also discussed and are informed by psychological, behavioral, and geographical profiling. References