As the microstructure of a material is refined from the micron scale to the nanoscale there is a significant increase in the interface density of the material. If the density of interfaces is high enough, the macroscopic deformation response can be influenced by the structure of the interface at the nanoscale. Shown below is a comparison of two interface types, cube-on-cube and incoherent twin. In the cube-on-cube interface structure the deformation systems are aligned across the interface as is indicated by the identical orientations of the Thomson tetrahedron on both sides of the bi-metallic interface. Alternatively the incoherent interface has a single aligned deformation plane as indicated. The mechanical response is shown for materials that consist predominantly of cube-on-cube and incoherent twin orientation illustrating the difference in material response that can be elicited based on interface structure.