This chapter examines how social context and individual vulnerabilities converge in the development of serial killers. Drawing on research in psychology, criminology, and developmental science, it shows that rates of physical, sexual, and psychological abuse are markedly higher among serial offenders than in the general population. Early maltreatment disrupts secure attachment, emotion regulation, empathy, and trust, capacities that normally restrain aggression. Learning processes within coercive families and deviant peer groups further shape stable “scripts” for aggression, while conduct-disordered behaviors (e.g., animal cruelty, fire-setting) are treated as indicators of severe developmental disturbance rather than deterministic precursors to homicide. Biological influences, genetic liability, neurodevelopmental insults, and sex-linked differences are presented as moderators that heighten sensitivity to harmful environments, not as standalone causes. The evidence supports a cumulative risk model: the likelihood of serial violence rises as multiple, severe risks co-occur, whereas protective factors, stable caregiving, effective school and community supports, and targeted interventions, can redirect trajectories. The chapter closes with prevention and policy implications focused on early detection of maltreatment and conduct problems, contingency-changing interventions (e.g., multisystemic and trauma-focused care), and strengthening social safety nets.