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.