This two-part book Volume on Semiconductor Metamaterials will survey the state-of-the-art in material platforms for optical metasurfaces. Part 1 will focus on materials for active metasurfaces, including tuning and sensing applications and will include chapters on Phase-Change Materials, Phase-Transition Materials and Soft Matter materials, as well as metasurface materials for polarization sensing, catalysis and chemical reactions. Part 2 will focus on static metasurfaces for light generation and detection. Materials employed for light emitting metasurfaces, metasurfaces operating in the ultraviolet, visible and infrared regions and metasurfaces from c² materials will all be discussed.