Irene Beyerlein Los Alamos National Laboratory For decades, severe plastic deformation has been successfully employed to refine the microstructure of metals and to fabricate nanostructured metals in bulk. It has recently been shown that a highly oriented microstructure develops during severe plastic rolling deformation of fcc Cu/bcc Nb nanocomposites. The deformation textures significantly deviate from that expected when rolling Cu or Nb alone and the prevailing Cu/Nb interfaces do not correspond to those with the lowest possible formation energies. High resolution TEM and atomic scale simulation find that these interfaces are, however, structurally ordered and relatively free of extrinsic defects, despite having experienced extremely large strains. Furthermore, we find that the interfaces are remarkably stable under further mechanical deformation and elevated temperatures (close to the melting temperature of Cu), giving the material unprecedented hardness, strength, and thermal stability compared to other nanostructured materials. The unusual and interesting behavior of these nanocomposite materials is attributed to interface-mediated deformation mechanisms. Atomic to meso-scale modeling are employed to reveal the relationship between the type of interfaces present in the nanomaterial, their lengthscales, and important plastic deformation mechanisms like dislocation slip, interface sliding, and deformation twinning. While we have made some progress in the area of structure-property relations for interfaces, little is still known about how interfaces evolve during the fabrication process. Last, we will present our atomic-to-meso-scale modeling efforts towards determining why bimetal interfaces have self organized into a single stable form that prevails over the entire nanocomposite material.