This book set out to examine how International Relations has begun to come to terms with the entwinement of social and natural systems. In a sense it is mysterious that this entwinement ever disappeared from view. Natural features of the world were originally the central focus of 19th century thinking about geopolitics (e.g. Mackinder 1904), and world politics is by definition a spatial and geographically located affair. Still, the modern discipline of IR, like many social sciences, almost lost sight of nature, rediscovering it gradually from around the 1960s in the form of ‘environmental problems’. In this concluding chapter, we first summarise the contribution of this volume to IR and the field of Global Environmental Politics. We also draw attention to additional themes and theories that define the field while lying beyond the scope of this volume. We then summarise what we see as the most prominent shifts in the study and practice of international environmental politics over the past two decades. We conclude the book with some reflections on the challenges that remain for the discipline of IR to fully appreciate the implications of the natural world and planetary singularity.