According to the recently published 2015 Lancet Commission on Health and Climate Change, the effects of global warming are set to undermine much of the global public health gains from the past century.1 But the message of the Lancet Commission is also hopeful, highlighting the leadership role that health professionals can play in addressing the crisis. Its central finding is that “tackling climate change could be the greatest global health opportunity of the 21st century.” How can this opportunity for public health be realized? Could negotiators gathering in Paris at the climate talks in December become ambassadors for a better and healthier future? We argue that they candindeed, the Paris climate talks offer an extraordinary opportunity that should not be squandered. The negotiators have the potential to deliver the most important public health treaty of the century