This chapter reviews the social neuroscience literature on human aggression, including research in molecular genetics, neuroendocrinology, neuroimaging, and social psychology. The findings indicate that (1) the amygdala and orbitofrontal cortex (OFC) are critical components of the neural circuitry of aggression; (2) the serotonergic system plays a crucial role in modulating aggression; (3) testosterone and cortisol influence aggression, likely through modulation of the amygdala and orbitofrontal cortex; and (4) environmental risk factors (media violence) and protective factors (emotion regulation) may modulate aggression via alterations in these biological systems and neural circuits. We end the chapter by discussing new directions for future research.