This book provides an overview of the evolution from previous-generation to next-generation communication networks, highlighting the key drivers and requirements for this transformative shift in wireless networks. Covering a wide range of topics including 5G and beyond, Internet-of-Things (IoT), Artificial Intelligence (AI), and emerging communication technologies such as visible light communication (VLC) and terahertz communication, orthogonal time-frequency space (OTFS) modulation, intelligent reflecting surfaces (IRS), this book offers insights into the latest advancements and innovations driving the development of next-generation communication systems. The book begins by examining the fundamental concepts and principles underlying current communication networks, providing readers with a solid understanding of the technological landscape. It then delves into the key challenges and opportunities presented by next-generation communication technologies, exploring topics such as multiple access, network architecture, security, and privacy.