A new model for the structure of mineralized bone collagen is presented which is compatible with neutron diffraction, electromicroscopic, crosslinking, and composition-density data. Mineralized collagen fibrils are comprised of azimuthally oriented, flexible molecules laterally arranged on a superlattice. Four nearest neighbors are longitudinally staggered by 67 nm and two neighbors by 2* 67 nm. In early stages of mineralization the molecules are parallel to the fibril axis with an average interaxis distance of 1.8 nm. In later stages they become flexed away from the fibril axis by an anisotropic lateral compression of molecules to an interaxis distance of 1.3 nm. Three quarters of the mineral in bone is disposed within the fibrils with a symmetry and habit reflecting the above organization of the collagen molecules.