This book examines polymer nanocomposites filled by inorganic nanofillers. Polymers are considered as nanocomposite matrix only, possessing, as a rule, an invariable structure. In many respects this situation is explained by the absence of a quantitative structural model of polymers amorphous state. This problem becomes particularly important because all structural elements of polymers have sizes of nanometer scale. The development of notions about polymers amorphous state structure within the frameworks of the cluster model of this structure allows to represent amorphous polymer as a quasitwophase system.