Intersectorality has long been presented as essential to improving human health. Yet its meaning, practice, and limits remain insufficiently examined. This book offers a systematic exploration of how intersectoral thinking emerged, why it has proved difficult to translate into practice, and how it can be reimagined for contemporary human, urban, and ecological health challenges. It traces modern intersectorality to emancipatory movements of the 1960s and 1970s and historically locates its first formal call to action. Throughout the text, these foundations of intersectorality provide a backdrop for social and political analyses that cast the net wider to include life, planetary and ecohealth perspectives in urban contexts, or 'One Urban Health'. The analyses are extended beyond human approaches to collaboration, to ecological governance and Indigenous cosmologies. The time has come to listen and to make meaningful changes to how the health and wellbeing of all and everything must be regarded. This book is also available open access on Cambridge Core.