Aggressive behavior is a universal phenomenon through time and space. This entry reviews interpersonal aggression, defined as behavior intentionally [Page 29]targeted to hurt another person, rather than intergroup or societal conflicts such as warfare. All human cultures exhibit a range of aggressive behaviors. This range encompasses physical, verbal, relational, and more recently, cyber types of aggression. However, cultures vary considerably in the incidence of different types of aggression and exhibit gender differences. Various factors help us to understand these differences, including descriptions and definitions of aggression; the encouragement, tolerance, or prohibition of various forms of aggression; and organizational and technological factors.