Metamaterial is an artificially constructed material that interacts differently with light and sound waves than standard natural materials. The book gives a comprehensive overview of metamaterials and their properties and the most prevalent structural designs for microwave and terahertz frequencies. The authors introduce new coding metamaterial for specific absorption rate (SAR) reduction applications in 5G Cellular Networks. They present conventional metamaterial with unique properties, ultra-thin, wide-band and mu-negative (MNG) characteristics for terahertz frequency application. The authors explore radiation protection, spanning fundamental concepts to the latest technologies, critically analyze how metamaterials contribute to the enhancement of safety and precision in radiation therapy. They cover metamaterial absorbers, navigate the domain of coding metamaterials, emphasizing their distinctive properties and pivotal role in RCS reduction and EMI shielding.