Polymer nanocomposites have drawn extensive attention due to the scope of tuning of phyisicochemical properties of the materials for high and specific applications. Preparation of polymer nanocomposites gives choice to choose appropriate polymer and type of nanofiller and processing parameter depends on applications. Polymer composites have wide use, from high-end application to low-end application. In this chapter, studies have been carried out on properties and applications of polymer nanocomposites in the field of bioelectronics besides highlighting on engineering applications which include high-performance composites even used in aerospace application.