Prompted to think about aggression and violence, we may recall a personal incident, a friend’s trauma, a community incident, or recent news.

The vividness of these personal or recent events may overshadow the many kinds of aggression and violence that people experience as individuals, groups, communities, and nations.

• As the result of violence, 1.6 million people die each year; countless more suffer physical and psychological injuries.

• In the twentieth century, 191 million people died in wars; more than half were civilians.

• In 2000, 200,000 young people died of violence; twenty to forty times that number had violent injuries requiring hospital treatment.

• For nonfatal violence, boys are more often victims of beatings than girls, while girls are more often victims of infanticide, neglect, and coerced prostitution than boys. In some countries one out of four women are abused by an intimate partner and one third of adolescent girls endure forced sexual initiation.

• Elderly people are at risk of physical, sexual, psychological, and eco­nomic violence.

As these statistics indicate, violence has many forms. It can be obvious or hidden, direct or structural, and it can be narrowly focused or pervasive. It can occur at all levels of analysis, from within an individual to between nations. Within these broad classifications, aggression and violence can be:

• Physical/symbolic. It is physical in assault and sexual abuse; it is sym­bolic in verbal, psychological, and emotional abuse.

• Vigorous/passive. It is vigorous in attacks; it is passive in the withhold­ing or diverting of needed resources.

• Means/end. It is instrumental when it is a means to obtain valued goods or goals; it is an end in itself in sadistic, dominating behavior.

• Sanctioned/prohibited. It is sanctioned when it is authorized by public officials to wield, consolidate, and abuse power; it is prohibited when it is unlawful, abhorred, and punished.

• Self-inflicted/inflicted on others. It is self-inflicted when it is directed at oneself as injury or suicide; it is often directed at others.

• Preserving/changing the status quo. It can protect the political status quo; it can be used to accelerate social change.

• Prosocial/antisocial. It can be described as bringing about a better soci­ety; it can be described as destructive to people, security, and the physi­cal and social infrastructure.

This chapter invites the reader to think about aggression and violence broadly, as complex constructs, rather than narrowly or stereotypically. Theories and research on aggression and violence offer an understanding of their nature, scope, and role in human experience.

When faced with aggression and violence in our lives or in the news, we may rely on readily available, simple, and stereotypical causal explanations. Theo­ries and research on aggression and violence offer a more complex under­standing of the origins of aggression and violence. The first section of this chapter is organized by an ongoing debate on the origins of aggression and vio­lence: do they result from nature or nurture? This section begins with theories emphasizing the biological and dispositional origins of aggression and violence. It then describes theories emphasizing the interaction of nature and nurture, and theories emphasizing nurture or social context. Social context is particu­larly important because it influences forms that aggression and violence take, and it can ameliorate inborn tendencies.

Research and theory on aggression and violence have primarily focused on their biological, motivational, and cognitive roots, but the influence of morals, norms, and values has received less attention. The chapter’s second section describes moral theories and discusses the importance of norm violations, moral judg­ment, disengagement of moral controls, moral exclusion, and structural violence to an understanding of aggression and violence. The chapter concludes with impli­cations of theory and research for practice, and it describes approaches that seek to reduce aggression and violence.