Polymer-clay systems are the only nanocomposites prepared from natural materials. They consist of polymer matrix and aluminosilicate platelets with sizes of 100 - 200 nm and thicknesses of 0.6 - 1.0 nm. In general, the clay nanocomposites, when compared with microcomposites, have better mechanical and optical properties, higher thermal stability and lower permeability to gases. The paper deals with the structure and properties of clay precursors and with the methods of preparation of the nanocomposites..