This book is devoted to the development of the local gradient theory of dielectrics. It presents a brief description of the known approaches to the construction of generalized (integral- and gradient-type) continuous theories of dielectrics. It describes a new continuum-thermodynamic approach to the construction of nonlinear high-order gradient theory of thermoelastic non-ferromagnetic polarized media. This approach is based on accounting for non-diffusive and non-convective mass fluxes associated with the changes in the material microstructure. Within the linear approximation, the theory has been applied to study transition modes of the formation of near-surface inhomogeneity of coupled fields in solids, disjoining pressure in thin films, etc. The theory describes a number of observable phenomena (including the surface, size, flexoelectric, pyroelectric, and thermopolarization effects in centrosymmetric crystals, the Meads anomaly, the high frequency dispersion of elastic waves, etc.) that cannot be explained within the framework of the classical theory of dielectrics.