Robert W. Balluffi has spent a rich research lifetime critically investigating and elucidating the atomic-scale defect structures of materials. Now, a new class of ultrafine-grained materials has been created in which such defects exercise a dominant role. The structures of these new nanophase materials, both metals and ceramics, have been investigated over the past several years by a wide range of experimental methods. These studies have included observations by X-ray and neutron scattering, transmission and scanning electron microscopy, Mössbauer, Raman and poistron annihilation spectroscopy and, most recently, scanning tunneling and atomic force microscopy and nuclear magnetic resonance. While the experiments have yielded considerable useful information about the structures of nanophase materials on a variety of length scales, much about the local atomic arrangements in the grains and interfaces of these materials remains to be elucidated. The present status of our knowledge of these structures is reviewed and some future research needs and opportunities are considered.