In this book, we study the dynamically vulcanized nanocomposite thermoplastic elastomers (TPV nanocomposites) prepared by a three-step melt mixing process. Uncured nanocomposite thermoplastic elastomers (TPE nanocomposites) were also prepared using a one-step melt mixing method. Three types of polypropylene (PP) with different melt flow index, an ethylene propylene diene monomer (EPDM), a maleic anhydride modified polypropylene (PPMA) as compatibilizer, and an organo-clay (Cloisite 15A) were employed in this work. The second part of this work is devoted to study the rheological and morphological properties of the dynamically vulcanized nanocomposite thermoplastic elastomers (TPV nanocomposites), based on EPDM and PP containing 20, 40, and 60 wt % of the rubber at 2 wt % of the clay. In the third part of this study, we examined the microstructure, rheology, and mechanical properties of the uncured nanocomposite thermoplastic elastomers (TPE nanocomposites) prepared by a one-step melt mixing process.