No one knows ITER’s true cost, which may be incalculable, but estimates have been rising steadily, and a conservative figure rests at twenty billion dollars, a sum which makes ITER the most expensive scientific instrument on Earth. But if it is truly possible to bottle up a star, and to do so economically, the technology could solve the world’s energy problems for the next thirty million years, and help save the planet from environmental catastrophe. Thirty-five countries, representing more than half the world’s population, are invested in the project, which is so complex to finance that it requires its own currency: the ITER Unit of Account.