'One World - One Health' is a developing concept which aims to explicitly incorporate linkages between the environment and human society into wildlife and human health care. Past work in the field has concentrated on aspects of disease, particularly emerging zoonoses, and focused on terrestrial systems. Here, we argue that marine environments are crucial components of the 'One World - One Health' framework, and that coral reefs are the epitome of its underlying philosophy. That is, they provide vast contributions to a wide range of ecosystem services with strong and direct links to human well-being. Further, the sensitivity of corals to climate change, and the current emergence of a wide range of diseases, make coral reefs ideal study systems to assess links, impacts, and feedback mechanisms that can affect human and ecosystem health. There are well established protocols for monitoring corals, as well as global networks of coral researchers, but there remain substantial challenges to understanding these complex systems, their health and links to provisioning of ecosystem services. We explore these challenges and conclude with a look at how developing technology offers potential ways of addressing them. We argue that a greater integration of coral reef research into the 'One World - One Health' framework will enrich our understanding of the many links within, and between, ecosystems and human society. This will ultimately support the development of measures for improving the health of both humans and the environment.