The present book deals with the phenomena of photoelectret and related properties such as photoconductivity, electroluminescence and photodielectric effect in certain composites. Study of the photoelectret properties has been made to explore the polarization characteristics and conditions of maximum polarization in composites of certain polycrystalline inorganic compounds. The photoconducting properties of these composites have been studied to determine the nature and distribution of traps and recombination centres, position of Fermi level and various other physical parameters. The electroluminescence studies have also been made and effect of applied voltage and frequency, conductance and capacitance, spectral response etc. have been studied. The change in conductance, capacitance and loss factor has been studied in dark and under illumination. The role of temperature has also been studied. The befitting explanation is given for various results observed under existing theories.