This paper will present details of interfacial design, structure and properties in a variety of different nanocomposites. The materials discussed include co-sputtered nanoscale Ag/SiO2 and Ag/Si thin films which exhibit novel optoelectronic behaviour, and melt spun nanoscale Pb/Al and Sn/Al sheets which exhibit novel mechanical behaviour. The relationships between processing, structure and properties are discussed for these unusual materials systems.