The forthcoming World Summit on Sustainable Development is an unprecedented opportunity to place health higher on the environmental and development agenda. The world's leaders will be grappling with some of the major challenges of our times--how to eradicate poverty and meet the world's development needs in a way that does not destroy the environment. Topping the agenda are water, energy, health, agriculture, and biodiversity. Improvement of access of the world's poor people to clean water, sanitation, and safe sources of household energy would have a huge effect on the main killers of young children--pneumonia and diarrhoea. Similarly, improved environmental management could substantially affect many infectious disease outcomes. At the same time, the growing epidemic of non-communicable diseases could be reversed if people's consumption patterns and lifestyles could be put on a more sustainable and healthy footing. A shared health, environmental, and development agenda could address the large share of the burden of disease that is environmentally related, and vice versa. The health sector increasingly needs to work in partnership with others rather than work alone. New tools are needed to ensure that intersectoral action becomes embedded in the way that the health sector does business. Improving coordination might be one of the most important ways in which we can help put the planet back on a healthy and sustainable path.