This chapter continues the exploration of biological causes of aggression and violence. It addresses the effects of different regions of the brain, including limbic and cortical structures; neurotransmitters; and, hormones, on aggression and violence. For all of these putative biological causes of aggression, caution is warranted due to the mixed evidence and the tendency to adopt overly simplistic models of biological causation. The implications for prevention and treatment are briefly discussed, but are dealt with in much more detail in Chap. 11, Individual Biological Interventions for Violence and Aggression. Psychopharmacology and Hormonal Treatments and Chap. 12, Individual Biological Interventions for Violence and Aggression. II. Other Biological Treatments.