This paper focuses on polymer nanocomposites and their syntheses, properties and future applications, several of these application will be successful in the near future. This new type of materials, based on smectite clays usually rendered hydrophobic through ionic exchange of the sodium interlayer cation with an onium cation, may be prepared via various synthetic routes comprising exfoliation adsorption, in-situ intercalative polymerization and melt intercalation. The whole range of polymer matrices covered, i.e., thermoplastics, thermosets and elastomers. Small addition - typically less than 6 wt%-of these nanoscale inorganic fillers promote concurrently several properties of the polymer materials, including tensile characteristics, heat distortion temperature, scratch resistance, gas permeability resistance, and flame retardancy. (C) 2004 Kluwer Academic Publishers.