Although no doubt a useful adaptation in our early evolutionary history, aggressive behavior contributes to many significant contemporary social challenges, ranging anywhere from bullying to homicide. Like any complicated human behavior, it is the outcome of complex neural and endocrinological systems operating within a dynamic social environment. In this chapter, we review many of the systems associated with aggression as well as their interactions and genetic correlates. We then present the environmental variables most associated with eliciting its behavioral expression. Common psychological interventions that have been developed to mitigate such expression are discussed, and we conclude with suggestions for future research in the field.