The positions of all the atoms in a sample of a metallic glass have been measured experimentally — fulfilling a decades-old dream for glass scientists, and raising the prospect of fresh insight into the structures of disordered solids. If the chemical element and 3D location of every atom in a material are known, then the material’s physical properties can, in principle at least, be predicted using the laws of physics. The atomic positions of crystals have long-range periodicity, which has enabled the development of powerful methods that combine diffraction experiments with the mathematics of symmetry to determine the precise atomic structure of these materials. Moreover, deviations from periodicity that create defects in crystals can be imaged with sub-ångström resolution. But these methods do not work for glasses, which lack long-range periodicity. Our knowledge of the atomic structure of glasses is therefore limited and acquired indirectly. Writing in Nature, Yang et al.1 report the experimental determination of the 3D positions of all the atoms in a nanometre-scale sample of a metallic glass.