Remarkable progress in the synthesis of nanoparticles along with their functionalization and assembly into “multi-material” architectures has enabled new domains of optical, electronic, and magnetic material properties to be accessed. A remaining grand challenge is to build these unique properties into inorganic “hard” materials that can be fabricated in sufficient quantities, and that possess the requisite stability for operation in engineering environments. Several collaborative projects in this area aim to develop a unifying set of experimental and theoretical techniques that enable the design, creation and control of the structure of biphasic functional materials. Unique properties will be achieved via directed, spontaneous synthesis paths that result in robust, morphologically stable two-phase nanoscale architectures that exhibit unusual thermal, magnetic, or radiation-resistant properties.