Polyhedral Oligomeric SilSesquioxanes (POSS) are structurally well defined cage-like molecules represented by the generic formula (RSiOl.5)n. POSS compounds possess a unique hybrid composition with an oxygen to silicon ratio of 1.5, intermediate between that for silica and silicone. An entire monomer catalogue (chemical tree) of hybrid POSS-based reagents suitable for polymerization and grafting reactions has been developed from R7Si7O9(OH)3 and related precursors. POSS reagents containing no more than one or two reactive groups enable the preparation of hybrid materials with desirable physical properties such as thermoplasticity, and elasticity. An overview of the synthesis of POSS monomers and thermoplastic POSS-acrylic polymers is given. The thermal and physical properties for POSS-acrylic monomers, homopolymers, copolymers, and blends with poly(methylmethacrylate) are described.