This essay details the historical progression of theories attempting to explain human aggression and victimization across the lifespan. Different theoretical lenses allowed for a comprehensive examination of the nuances between aggression and victimization, as supported by landmark experimental research studies conducted in the social and behavioral sciences. In addition, the neurobiology of aggression was discussed as an area of future research where professionals from multiple fields could collaborate in order to better understand the intersection of biology and the environment and how it impacts the development of individuals.

Human history is replete with chronicles of wars and interpersonal aggression. Much of the news we read describe aggressive actions toward individuals or groups of people, within and between political and religious factions, and among countries around the globe. In this essay, we provide an overview of what we know about this ubiquitous human behavior.

First, we define important terms. Aggression refers to deliberate acts that inflict harm; victimization is the experience of receiving unwanted aggressive acts. Physical aggression (use of physical force toward another, such as hitting and kicking) is a form of direct aggression, as is verbal aggression (name-calling, malicious teasing). More recently, relational (indirect) aggression (Crick, 1995) has been identified as a distinct form of aggression in which the target's social relationships or status are attacked (e.g., social exclusion, rumor spreading). There is debate about whether cyber-aggression is a separate form of aggression or a method for delivery of aggressive actions (see Bauman, Cross, & Walker, 2013, for discussion of this issue). Aggression can also be categorized by the motive behind the action: proactive aggression includes hostile aggression, in which the desire to harm the target drives the behavior, and instrumental aggression, which refers to acts calculated to bring valued resources to the aggressor, whereas reactive aggression is provoked by an actual or anticipated aggressive attack and is enacted in self-defense or retaliation (Hartup, 2005). Researchers sometimes distinguish between trait aggression, which is a characteristic of a person across time and settings such that the person is more prone to commit acts of aggression than others, and state aggression, which refers to a momentary experience of aggression in a particular situation or context.