The discovery of amorphous, or glassy, metallic alloys in 1959 posed an intellectual challenge. How can one describe the structure of glasses when there is no long-range periodicity? What can the structure tell us about why certain metal alloys form glasses more easily than others? First, some universal characteristics, if any exist, of the structure metallic glasses needed to be found. A convincing model was proposed for the structure of metallic glasses based on Bernal’s dense random packing (DRP) structure. Central to this proposal is the idea that the structure of metallic glasses is that of the random filling of space by non-interacting identical spheres. In this model, strongly directional interatomic bonds do not play an important role in determining the structure of metallic glasses. This model is hpwever in conflict with one proposed by Chen, which correlates increased glass formability with increased chemical interaction between dissimilar atoms.