Amyloid fibrils formed from different proteins, each associated with a particular disease, contain a common cross-β spine. The atomic architecture of a spine, from the fibril-forming segment GNNQQNY of the yeast prion protein Sup35, was recently revealed by X-ray microcrystallography. It is a pair of β-sheets, with the facing side chains of the two sheets interdigitated in a dry 'steric zipper'. Here we report some 30 other segments from fibril-forming proteins that form amyloid-like fibrils, microcrystals, or usually both. These include segments from the Alzheimer's amyloid-β and tau proteins, the PrP prion protein, insulin, islet amyloid polypeptide (IAPP), lysozyme, myoglobin, α-synuclein and β₂-microglobulin, suggesting that common structural features are shared by amyloid diseases at the molecular level. Structures of 13 of these microcrystals all reveal steric zippers, but with variations that expand the range of atomic architectures for amyloid-like fibrils and offer an atomic-level hypothesis for the basis of prion strains.