The biological and physical environment of the planet is changing at an unprecedented rate as a result of human activity, and these changes may have an enormous impact on human health. One of the goals of human development is to protect health in the face of rapid environmental change, but we often fail to do this. The aim in this paper is to distinguish between socioeconomic aspects of development that are likely to be protective and those that are likely to increase vulnerability (the capacity for loss resulting from environmental change). Examples include climate change in the Pacific. We conclude that protecting human health in a changing world requires us to take steps to minimize harmful change wherever possible, and at the same time to be prepared for surprises. The goals of mitigation (reducing or preventing change) and adaptation (response to change) are not mutually exclusive. In fact, steps to make populations more resilient in the face of change are often similar to those that are needed to lighten the load on the environment. We need social policies that convert economic growth into human development. Wider application of sustainable development concepts is part of the solution. In particular, there is a need to promote health as an essential asset of poor and vulnerable populations. It is their key to productivity and to surviving shocks; it is also the key to achieving broader development goals such as universal education. For these reasons it is in the interests of all sectors--economic, social and environmental--to play their particular roles in protecting and improving health.