Experimental studies on the electronic and optical properties of conductingpolymer thin films are reviewed. Conducting polymers have been processed into various forms of undoped and doped thin films. The electrical conduction properties have been characterized by conventional transport measurements as well as by the fabrication and evaluation of polymeric semiconductor devices. Important electrical and structural material parameters are extracted by fitting the results to conductivity models. Optical and electro-optical measurements give valuable information on the structural order, the electronic structure, and the unusual nature of charge carriers in these novel materials. The polymeric devices are mainly utilized in material characterization, but possible implications for applications are also discussed.