This chapter discusses the electrical conductivity of polymers. The chapter presents a review of the intrinsic properties of the metallic state of a broad class of conducting polymers with emphasis on the universality in the observed behaviors. It then provides a brief overview of conductivities of various conducting polymers, and a summary of the models for the insulator-metal transition, localization, and metallic conductivity; structural order results of x-ray diffraction studies. The next section presents a review of the surveys of metallic density of states of highly conducting polymers and the results of temperature-dependent dc conductivity, thermoelectric power, and microwave dielectric constant. The following sections discuss the optical properties, transmission, and reflection of the highly conducting state, and describe the ultimate conductivity of conducting polymers including resonance quantum transport in doped conducting polymers. New morphologies nanostructuring of conducting polymers such as fibers, and applications of conducting polymers including an electric field effect are also discussed.