Progress in addressing increasing levels of violence globally will require action and leadership from cities. In this introduction, we give grounding to the genesis of this volume, its purpose and components, and key concepts to guide the reader. We describe the core challenges and opportunities related to violence reduction and offer a novel framework of identity-based mass violence as an important analytical lens, which brings together the fields of atrocity prevention, urban violence, and peacebuilding and highlights their converging pathways. With the majority of violence occurring outside of conflict zones, how should we unpack the systems and structures that enable large-scale and widespread violence to persist? This opening positions the volume as an important contribution to research, policy, and practice, one that squares off directly against the preexisting failures of collaboration until now, including a lack of recognition of the magnitude of such violence. We evoke a hopeful message, drawn from academia, practitioner knowledge, and voices from those who have experienced such violence and transformative healing first-hand. As the reader, you are invited to engage deeply with the evidence and stories presented in this volume.