Earth's natural systems represent a growing threat to human health. And yet, global health has mainly improved as these changes have gathered pace. What is the explanation? As a Commission, we are deeply concerned that the explanation is straightforward and sobering: we have been mortgaging the health of future generations to realise economic and development gains in the present. By unsustainably exploiting nature's resources, human civilisation has fl ourished but now risks substantial health eff ects from the degradation of nature's life support systems in the future. Health eff ects from changes to the environment including climatic change, ocean acidifi cation, land degradation, water scarcity, overexploitation of fi sheries, and biodiversity loss pose serious challenges to the global health gains of the past several decades and are likely to become increasingly dominant during the second half of this century and beyond. These striking trends are driven by highly inequitable, ineffi cient, and unsustainable patterns of resource consumption and technological development, together with population growth. We identify three categories of challenges that have to be addressed to maintain and enhance human health in the face of increasingly harmful environmental trends. Firstly, conceptual and empathy failures (imagination challenges), such as an over-reliance on gross domestic product as a measure of human progress, the failure to account for future health and environmental harms over present day gains, and the disproportionate eff ect of those harms on the poor and those in developing nations. Secondly, knowledge failures (research and information challenges), such as failure to address social and environmental drivers of ill health, a historical scarcity of transdisciplinary research and funding, together with an unwillingness or inability to deal with uncertainty within decision making frameworks. Thirdly, implementation failures (governance challenges), such as how governments and institutions delay recognition and responses to threats, especially when faced with uncertainties, pooled common resources, and time lags between action and eff ect. Although better evidence is needed to underpin appropriate policies than is available at present, this should not be used as an excuse for inaction. Substantial potential exists to link action to reduce environmental damage with improved health outcomes for nations at all levels of economic development. This Commission identifi es opportunities for action by six key constituencies: health professionals, research funders and the academic community, the UN and Bretton Woods bodies, governments, investors and corporate reporting bodies, and civil society organisations. Depreciation of natural capital and nature's subsidy should be accounted for so that economy and nature are not falsely separated. Policies should balance social progress, environmental sustainability, and the economy. To support a world population of 9-10 billion people or more, resilient food and agricultural systems are needed to address both undernutrition and overnutrition, reduce waste, diversify diets, and minimise environmental damage. Meeting the need for modern family planning can improve health in the short termeg, from reduced maternal mortality and reduced pressures on the environment and on infrastructure. Planetary health off ers an unprecedented opportunity for advocacy of global and national reforms of taxes and subsidies for many sectors of the economy, including energy, agriculture, water, fi sheries, and health. Regional trade treaties should act to further incorporate the protection of health in the near and long term. Several essential steps need to be taken to transform the economy to support planetary health. These steps include a reduction of waste through the creation of products that are more durable and require less energy and materials to manufacture than those often produced at present; the incentivisation of recycling, reuse, and repair; and the substitution of hazardous materials with safer alternatives. Despite present limitations, the Sustainable Development Goals provide a great opportunity to integrate health and sustainability through the judicious selection of relevant indicators relevant to human wellbeing, the enabling infrastructure for development, and the supporting natural systems, together with the need for strong governance. The landscape, ecosystems, and the biodiversity they contain can be managed to protect natural systems, and indirectly, reduce human disease risk. Intact and restored ecosystems can contribute to resilience (see panel 1 for glossary of terms used in this report), for example, through improved coastal protection (eg, through wave attenuation) and the ability of fl oodplains and greening of river catchments to protect from river fl ooding events by diverting and holding excess water. The growth in urban populations emphasises the importance of policies to improve health and the urban environment, such as through reduced air pollution, increased physical activity, provision of green space, and urban planning to prevent sprawl and decrease the magnitude of urban heat islands. Transdisciplinary research activities and capacity need substantial and urgent expansion. Present research limitations should not delay action. In situations where technology and knowledge can deliver win-win solutions and co-benefi ts, rapid scale-up can be achieved if researchers move ahead and assess the implementation of potential solutions. Recent scientifi c investments towards understanding non-linear state shifts in ecosystems are very important, but in the absence of improved understanding and predictability of such changes, eff orts to improve resilience for human health and adaptation strategies remain a priority. The creation of integrated surveillance systems that collect rigorous health, socioeconomic, and environmental data for defi ned populations over long time periods can provide early detection of emerging disease outbreaks or changes in nutrition and non-communicable disease burden. The improvement of risk communication to policy makers and the public and the support of policy makers to make evidence-informed decisions can be helped by an increased capacity to do systematic reviews and the provision of rigorous policy briefs. Health professionals have an essential role in the achievement of planetary health: working across sectors to integrate policies that advance health and environmental sustainability, tackling health inequities, reducing the environmental impacts of health systems, and increasing the resilience of health systems and populations to environmental change. Humanity can be stewarded successfully through the 21st century by addressing the unacceptable inequities in health and wealth within the environmental limits of the Earth, but this will require the generation of new knowledge, implementation of wise policies, decisive action, and inspirational leadership.