Fullerenes enhance the photoconductivity of photoconductive polymers. This paper studies the mechansim of enhancement both experimentally and theoretically. The effects of fullerene doping on the spectroscopic, charge generation, and charge transport properties of the polymer are reported. Electrical field effects and magnetic field effects are examined. On the basis of these data a charge generation mechansim involving a singlet of weak charge-transfer complex is proposed for fullerene-doped N-poly(vinylcarbazole). A new theoretical model combining both the Onsager and Marcus theory is developed to quantitatively account for the field-dependent charge generation efficiency in nonpolar medium.