Global health, population growth, economic development, environmental degradation, and climate change are the main challenges we face in the 21st century. However, because the academics, non-governmental organisations, and policy makers in these specialties work within separate communities, our understanding of the associations between them is restricted. We organised an international symposium in May, 2011 in London, UK, for academics and technical experts from population, developmental, and environmental science to encourage debate and collaboration between these disciplines. The conference provided the impetus for this Review, which describes, in historical context, key events and fundamental intercommunity debates from the perspectives of population, development, and climate change communities. We consider the interconnections between population, development, and climate change and their effects on health, including new analysis of longstanding debates, and identify opportunities for effective collaboration on shared goals.