This volume brings together the understanding and the judgement of the world's scientific community on the issues of highest priority for the future of the environment and development. It looks beyond the state-of-the-art and formulates the environment and development research agenda, and identifies the scientific knowledge base which will be needed for rational policy decisions. Diverse topics such as population, land use, energy and global cycles are covered under sixteen themes which have been grouped into three sections: Problems of Environment and Development, Scientific Understanding of the Earth System, and Responses and Strategies. All the contributions were developed at an invited conference convened by the International Council of Scientific Unions and provide a significant input to the forthcoming UN Conference on Environment and Development.