Abstract Deregulation and new environmental requirements combined with the growing scarcity of fossil resources and the increasing world energy demand lead to a renewal of the debate on tomorrow's energies. Specifically, nuclear energy, which has undeniable assets, faces new constraints. On the one hand, nuclear energy is very competitive and harmless to greenhouse effect. From this point, it seems to be an ideal candidate to reach future objectives of sustainability, availability and acceptability. On the other hand, its technology of production — based on fission — remains imperfect and generates risks for environment and health. In this respect, it is less desirable. Therefore, world researchers turn today towards another type of nuclear technique, fusion, on which the project ITER is founded. This worldwide project is interesting for our analysis because, as a technological revolution, it takes into consideration all the global challenges of nuclear energy for the future, and particularly its capacity to meet the increasing energy needs of developing countries. It is the example par excellence of a successful international scientific collaboration oriented towards very long-run energy ends that involve huge technological, economic and political stakes. Focusing on this project, we thus have to reconsider the future place of nuclear energy in a more and more demanding world. Considering the magnitude of the efforts undertaken to implement ITER, this paper aims at analysing, in a detailed way, its goals, its challenges and its matter.