Clinical correlates of violent behavior are known, but the underlying mechanisms are not well understood. This article reviews recent progress in the understanding of such mechanisms involving complex interactions between genes, prenatal and perinatal environmental factors, and rearing conditions. Violent behavior is heterogeneous; that is, impulsive and premeditated violent acts differ in their origins, mechanisms, and management. Recent molecular genetic studies of neurotransmitter regulation are providing new insights into pathophysiology of violent behavior. Functional anatomy of neurotransmitters involved in the regulation of violent behavior is being studied with recently developed brain imaging methods. Increasing evidence indicates commonalities between the neurobiology of violent and suicidal behavior. Progress in the prevention and management of violent behavior depends on studies that address biological factors in their social context. This article updates a previous review.