This review aims at reporting on very recent developments in syntheses, characterization, properties and future applications of polymer-layered silicate nanocomposites (PLSN). 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, melt intercalation and template synthesis.  The whole range of polymer matrices is covered, i.e. thermoplastics, thermosets and elastomers. Two types of structure may be obtained, namely intercalated nanocomposites where the polymer chains are sandwiched in between silicate layers and exfoliated nanocomposites where the separated, individual silicate layers are more or less uniformly dispersed in the polymer matrix. Because of the nanometer size dispersion of clay, this new family of materials exhibits markedly improved properties when compared with the pure polymers or conventional composites at very low filler level, usually inferior to 5 wt.%. These include increased modulus and strength, decreased gas permeability, increased solvent and heat resistance and decreased flammability. They are already commercially available and applied in car and food packaging industries. Undoubtedly, the unique combination of their key properties and potentially low production costs pave the way to a much broader range of applications.