The Second Volume is mostly devoted to the specific properties of active dielectrics. A dielectric may be considered as active if it can convert energy or information. Active (or adaptive, or controlled, or smart) dielectrics may easily react to the changes of temperature, pressure, mechanical stress, electrical and magnetic fields and light illumination. Active dielectrics are classified as pyroelectrics, ferroelectrics, piezoelectrics, electrets, quantum-electronics materials; as well as on posistors, superionic conductors, liquid crystals and others. The nature of spontaneous polarization is the main topic of book. A number of electrical, mechanical and thermal effects of polar crystals are considered, and a reductive model of crystals internal polarity is proposed. The relationship between pyroelectricity and piezoelectricity is discussed on the basis of experimental and theoretical data. Various types of pyroelectrics, ferroelectrics and ferroelastics are described. The non-linearity of ferroelectrics and paraelectrics is analysed.