Interface Design in Polymer Nanocomposites – The emergence of polymer nanocomposites began with the discovery at Toyota in the 1980's that small additions of nanoclay to nylon-6 resulted in dramatic increases in strength, modulus, heat distortion temperature, and gas barrier properties relative to unreinforced thermoplastics. Since then, nanocomposite technology has expanded to include polymers reinforced with carbon nanotubes (CNTs), graphene, and a host of other fillers that not only increase mechanical properties, but also add new functionalities. The success of these efforts has taught that vast enhancements are possible with relatively small additions (<5%) of nanofillers, primarily because of the generation of enormous interface area and the attendant constraints of those interfaces on nearby polymer mobility. However, these enhancements are generally not achieved without intelligent control of the interface chemistry, which is necessary to control dispersion and to facilitate mechanical coupling to the polymer matrix. The successes of nanocomposite research have raised the tantalizing prospect of integrating nanocomposites with conventional fiber composites, thus affording the opportunity for multi-scale design of hierarchical composites. Activities at USC’s Composites Center include efforts to functionalize multi-walled carbon nanotubes for specific polymer systems. Such surface modifications result in improved dispersion and in-situ formation of covalent bonds at the interface. Recent efforts have also focused on fabricating hierarchical epoxy nanocomposites, designing multi-functional nanocomposites for underwater acoustic structural applications, and exploring the effects of filler geometry.