'The publication of World in Transition: Towards Sustainable Energy Systems is timely indeed. The World Summit on Sustainable Development gave great prominence to this challenge, but failed to agree on a quantitative, time-bound target for the introduction of renewable energy sources. The German Advisory Council on Global Change (WBGU) has now produced a report with a global focus, which is essential in view of the global impacts of climate change. The report provides a convincing long-term analysis, which is also essential. Global energy policies have to take a long-term perspective, over the next 50 to 100 years, while providing concrete guidance for decision-makers to implement now.There is an urgent need to secure energy supplies for the 2.4 billion people who still depend upon traditional biomass, while avoiding dangerous climatic changes. Our one world must close the gap between industrialized countries' surfeit and developing countries' poverty. Policies will need to consider both the broader environmental and specific climate constraints. I recommend this book very warmly to everyone concerned with global energy issues' Klaus Topfer, Executive Director, United Nations Environment ProgrammeWorld in Transition: Towards Sustainable Energy Systems underscores the urgent need to transform global energy systems so that the world's population has access to energy based on renewable sources. This is necessary to protect the global climate and to free those in developing countries trapped by energy poverty. Such an approach would also yield a peace dividend by reducing dependence upon regionally concentrated oil reserves. The authors stress that such a reconfiguration of energy systems is both feasible and fundable if rapid and resolute action is taken in the coming two decades. To this end, they propose a roadmap with specific milestones, making this an indispensable contribution to the scientific and policy debates on these critical issues and essential reading for those engaged with them.