On 28 May 2009, at a closed meeting in Brussels, ministers and state secretaries of education and science from several EU countries decided to build the European Spallation Source (ESS) in Lund, Sweden. Or did they? It is common for big European science projects to be surrounded by secrecy and political deceit, but the ESS is extraordinary in its elusiveness. There is a remarkable lack of concrete ecomic, political, technical and scientific underpinnings to the project - but a boasting certainty in the promises of future paybacks. The ESS is an accelerator-based neutron spallation facility that will cost billions of Euros to build and run. It is expected to bring new kwledge in several fields including materials science, energy research, and the life sciences. But its financing is t yet certain, and future returns hard to predict. How then could the decision to build ESS occur? Why was there so little organized resistance? This book places the ESS project in its political and scientific context. It links the decisions taken to the history of Big Science in Europe and in Sweden. It looks at the dynamic political processes of establishing this megaproject in a small town in the south of Sweden. The eight chapters start from a paradoxical state of affairs: The ESS is t funded, and t formally decided in any binding agreements - yet it is treated as a future reality, locally and nationally, loaded with promises of scientific, ecomic and social returns. The book makes a much-needed first contribution to the analysis of the ESS project and its political, environmental, and social ramifications. It should be read by scholars of science and techlogy studies, politicians and the interested general public.