Although intrinsically conductive polymers were discovered in 1970s, their application is quite limited mainly due to their poor processability and low conductivity. Most of conductive polymers are insoluble in any solvent and cannot melt. Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) has gained great attention and considered as the most successful conductive polymer, because it can be dispersed in water and some polar organic solvents. But it has a problem of low conductivity. The as-prepared PEDOT:PSS films from its aqueous solution usually has a conductivity of less than 1 S/cm. Here, I will present several novel methods to significantly enhance the conductivity of PEDOT:PSS. The conductivity can be enhanced to be more than 3000 S/cm. Thus, highly conductive PEDOT:PSS can be used as the transparent electrode of optoelectronic devices like solar cells because it can have high transparency in the visible range. In addition, they can exhibit high thermoelectric properties.