Polyhedral oligosilsesquioxane (POSS)-based hybrid polymers have generated much interest recently, both from the academic and industrial points of view. POSS are completely defined molecules of nanoscale dimensions that may be functionalized with reactive groups suitable for the synthesis of new organic-inorganic hybrids, thus providing the opportunity to design and build materials with extremely well-defined dimensions possessing nanophase behavior. POSS have been successfully incorporated into common polymers via copolymerization, grafting or blending. A variety of POSS-containing copolymers have been prepared and they have displayed great potential in the development of a wide range of hybrid nanomaterials with diverse properties. This work has critically evaluated the recent developments in syntheses of POSS polymer materials leading to POSS nanocomposites. The syntheses of POSS cages, monomers containing POSS cages, POSS-dendrimers' cores, POSS-containing polymers (nano-building blocks) and POSS nanocomposites are described in detail. This work also assesses the properties of POSS nanobuilding blocks that can be otherwise used for developing nanocomposites. Such properties include mechanical, thermal, flame-retardant and viscoelastic properties. Investigations into the structure, morphology and compatibility of POSS nanobuilding blocks have been reviewed. Other properties covered include the ion-mobility and swelling characteristics as well as porosity of POSS nanobuilding blocks. Lastly, existing and possible future applications are highlighted and final conclusions are drawn.