Applicability of low-frequency dielectric methods of investigation of solid inhomogeneous structures are presented. The methods prove to be very useful for determination of physical properties of both inhomogeneous one-component and multi-component systems including systems arising as a result of adsorption of gases and liquids onto solid surfaces. It is also possible to study adhesion of composite components using the dielectric methods. The methods are particularly useful for investigations of ageing phenomena of polymer composites. The dielectric properties of two polycrystalline low-molecular weight organic compounds are presented as an example of investigations of one-component inhomogeneous structures.