Phase change memory materials are based on the astonishingly rapid and reversible transition between the amorphous and crystalline phases of nanosized “bits” in a very thin polycrystalline layer. These phases must also have contrasting resistivities or optical properties, and few materials satisfy all requirements. Great efforts over more than 20 years have brought focus on a few families of alloys, one of which (“GST”) contains germanium (Ge), antimony (Sb), and tellurium (Te). One such alloy that has been used in Blu-ray Disc optical storage is Ge8Sb2Te11 and 640-atom simulations of its amorphous phase are described in the Feature Article by Akola and Jones (pp. 1851–1860). The cover figure shows the structure that results (red: Ge, blue: Sb, yellow: Te). Fourfold rings where Te atoms alternate with Ge or Sb atoms are very common, and a three-dimensional “column” with such ordering is shown. The prevalence of fourfold rings of this type in both amorphous and crystalline phases is a crucial feature of GST phase change materials.