The Introduction explains that we now understand psychopathy as a personality disorder characterized by lack of empathy and guilt, manipulation of other people, a tendency to make bafflingly destructive life choices, and, in the case of criminal psychopathy, capacity for premeditated violent behaviour. It highlights that recent research into psychopathy has provided much information, but a lot also remains a mystery and a focus of continued research efforts. Key questions to be considered in the chapters that follow include: Is psychopathy a genetic condition? Do people become psychopaths because of their childhood experiences? How can we understand their behaviour? What are the warning signs of someone who is at risk of developing psychopathy? Can psychopathy be prevented or treated? Are all psychopaths criminals?