This introductory chapter introduces a redefined vision of urbanism that transcends the outdated divide between built form and natural systems. This first volume of a trilogy on Nature in Cities argues that cities cannot remain resilient, equitable, or liveable without fully embedding ecological principles into their identity, planning, and governance. Drawing from multidisciplinary perspectives, it frames nature not as an aesthetic addition but as critical infrastructure for health, climate resilience, inclusivity, and placemaking. The chapter begins by outlining the historical narrative of separation between cities and nature and its enduring consequences for urban vulnerability. It then establishes the transformative potential of ecological integration, showing how access to biodiverse landscapes supports public health and well-being, mitigates climate risks, and fosters social belonging. The book’s purpose is to clarify both intellectual aims and practical goals: bridging theory and practice, connecting disciplines, and cultivating a philosophy of care that reimagines the urban condition itself. Positioned within the global sustainability discourse, this work sets the stage for a long-term narrative of nurturing cities, places where ecological care becomes central to survival, justice, and dignity in our time.