Aggression and violent offending have severe and wide-reaching negative consequences for victims and wider society, prompting forensic psychologists and criminologists to investigate the factors that can underpin and predict this type of behaviour. This chapter outlines the distinctions between aggression and violence before explaining some of the fundamental theories that provide insight into why some people behave aggressively and violently while others do not. Following from these theoretical foundations, this chapter then discusses some empirically derived predictors of aggression and violence, including adverse childhood experiences, personality traits, emotion regulation and recognition and criminal attitudes. This chapter highlights how these factors intertwine to form a multidimensional understanding of aggression and violence, advocating for early intervention and tailored treatment approaches to mitigate the harms associated with violent offending.