While most animal studies of aggression concern aggressive behavior as a functional and adaptive behavior, studies in humans often focus on impulsive aggression and violence as maladaptive forms of aggressive behavior. Violence can be defined as a form of aggressive behavior that lacks its social communicative function. Little is known about the factors involved in the change from adaptive aggression into violence. A number of animal experiments will be discussed aimed at the interaction between individual predisposition and previous social experience in the development of violence. Ecological studies in feral populations of mice and birds show a functional bimodal distribution of high and low aggressive phenotypes. Subsequent field- and laboratory studies indicate that these phenotypes differ more generally in their response to any environmental challenge. This has led to the view that high and low individual levels of aggressive behavior reflect a proactive coping style or a reactive coping style respectively. The proactive coping style is characterised by a reduced dependence of environmental stimuli, i.e. they tend to develop routines. This capacity to develop routines seems to be the underlying factor in the development of violence. For example, an extensive sequential analysis of the pre-attack behavior of two interacting males shows that the aggressive behavior of the proactive animal becomes more and more independent of the opponent after repeated winning. Experienced, highly aggressive males no longer respond to social signals from the opponent and a reduced behavioral plasticity, leading to a violent form of aggression. There are a number of neurobiological and neuroendocrine correlates of the violent prone proactive coping style. The proactive animal is characterised by a high sympathetic reactivity, a strong negative relation between social experience and dependence of plasma testosterone, and low serotonergic transmission as a trait characteristic. It will be argued that understanding the behavioral and physiological mechanisms underlying the individual differentiation in behavioral plasticity contributes to a further understanding of the factors involved in the transition of aggression into violence and the capacity to cope with changes in the social environment.