This book explores the state-of-the-art advancements in the terahertz (THz), millimeter-wave (mm-wave), and infrared (IR) technologies. By bridging the gap between electronics and photonics, it explores wide-bandgap semiconductors, nanostructures, nanomaterials, photonic integration, and quantum confinement technologies, linking foundational physics with practical applications. Challenges such as scaling limitations, thermal management, and noise suppression are discussed alongside emerging solutions like artificial intelligence, metamaterials, and hybrid systems. The volume one caters to undergraduate and postgraduate students, researchers, and professionals seeking a comprehensive resource on cutting-edge innovations in communication, imaging, and sensing technologies.