The demand for lightweight, cost-effective electrically conducting polymers and conducting nanocomposites for various applications, such as sensors, actuators, etc., has been skyrocketing in recent years. Electrically conducting polymer composites (CPCs) can be developed by dispersing conducting particles in inherently conducting polymers or insulating polymer matrices. Due to the recent advancements in nanotechnology, it is possible to tailor make composite materials with exceptional electrical, mechanical and thermal properties. The properties of conducting polymer binary composites can be altered by careful selection and dispersion of fillers in the polymer matrix. In a similar way, conducting hybrid polymer composites for a particular application can be synthesized by exploiting the synergism in properties of two or more dispersed phases. It is not merely cost reduction that drives the market of CPCs but also environmentally benign synthesis procedures wherever possible and mass production of the end product with better energy savings has an immense influence on the demand for these materials. The unprecedented growth of nanotechnology offers better control over manipulation of filler size as well as polymers, and hence the composites can be tailor-made. Though there are many nanofillers, such as nanographite, carbon nanofiber, etc., in this chapter, more attention will be given to the electrical properties of multiwalled carbon nanotube (MWCNT) filled polyethersulfone (PES) conducting composites, along with that of PES-graphite-MWCNT hybrid nanocomposites. © 2018 Scrivener Publishing LLC.