Until about 30 years ago all carbon-based polymers were regarded strictly as insulators, and hence were extensively utilized by the electronics industry for this very property. They have been used as inactive packaging and insulating material. This very narrow perspective has rapidly changed with the emergence of intrinsically conducting polymers. The combination of conventional polymers with conductive polymers or fillers is an important alternative to obtaining new polymeric materials with designed properties. Through the combination of conventional polymers with conductive polymers such as polyaniline, polypyrrole, and so on, the mechanical properties of conducting polymers can be improved. The insulating polymer removes the brittleness and lack of processibility that are the main drawbacks hindering conducting polymers. Blend applications require that conductivity is achieved at a small weight fraction of conducting polymer. There is also an increased requirement for polymeric materials whose electrical conductivity can be tailored. The aim this chapter is to describe conducting polymer blend systems to identify characteristic trends that might be useful for the investigation of their potential application in various electronic and optoelectronic devices.