Ecosystem approaches to health (i.e. Ecohealth) arose in the 1990s as Canada wrestled with diverse problems ranging from Great Lakes contamination to zoonotic diseases. Ecohealth links population health with the environment and sustainable development. The approach is based on the understanding that health (good or bad) arises from inter-relationships between coupled human and natural (social-ecological) systems. To address multi-factorial, dynamic impacts on health, a new research paradigm was needed which would overcome the separation of humans and ecosystems. This paradigm shift embraces transdisciplinarity, social justice, gender equity, multi-stakeholder participation and sustainability. Rooted in systems thinking, it provides a framework to study and manage relationships between human beings and the environment in pursuit of co-benefits that simultaneously improve ecosystem health and human well-being. In 2004, a group of strategic thinkers formulated 12 Manhattan Principles calling for the international community to adopt an holistic approach to combat zoonotic ‘threats to the health of life on Earth’ under the banner ‘One World, One Health’, forming the Onehealth movement. With this, epidemiology - the science of population health - expanded its toolkit to embrace qualitative post-normal methods. These approaches are consistent with The Earth Charter and the mission of the Global Ecological Integrity Group.