This chapter introduces the complex and often overlooked concept of perpetrator trauma—the emotional and psychological distress experienced by individuals as a result of their own harmful actions. It draws on philosophical, historical and psychological perspectives to explore how trauma may arise from the perpetration of violence, including in military, gang and interpersonal contexts. The chapter challenges binary victim-perpetrator frameworks, arguing that recognising perpetrator trauma does not excuse harm but can be a critical entry point for intervention and prevention. It also suggests that those systems that typically ignore this form of trauma, are more likely to miss opportunities for meaningful rehabilitation, prevention and harm reduction. The chapter urges greater integration of perpetrator trauma into justice and mental health responses to break cycles of violence.