Nuclear fusion can be likened to God or the devil. Out there among the stars, it is godlike, creating atoms and giving birth to life. But down below, on earth, nuclear fusion is the devil: it has been used to make bombs that can annihilate everything, including all forms of life. Now that the devil of thermonuclear destruction seems to have been locked back in its box, nuclear fusion kept under tight control in civil reactors offers the hope for long-term economic development. Isnt it the only inexhaustible, non-polluting form of energy that offers no limits except that of human technical knowledge? Paul-Henri Rebut is a member of the Academy of Science.