The Internet of Things (IoT) is an interconnection of several devices, networks, technologies, and human resources to achieve a common goal. A variety of IoT-based applications are being used in different sectors and have succeeded in providing huge benefits to the users. As a revolution, IoT overtook the entire global landscape with its presence in almost every sector, including smart cities, smart grid, intelligent transportation, healthcare, education, and so on. This technological revolution also moved to the machines, converting them into intelligent computers that can make real-time decisions and communicate with each other, forming an Internet of Systems/Machines. The use of secure light-weight protocols will help us in developing environment-friendly and energy-efficient IoT systems. IoT is an emerging and recent area of research, adopted for many applications, and there is a need to investigate further challenges in all aspects of it. This book will provide information on fundamentals, architectures, communication protocols, use of AI, existing applications, and emerging research trends in IoT. It follows a theoretical approach to describe the fundamentals for beginners as well as a practical approach with the implementation of case studies for intermediate and advanced readers. The book will be beneficial for academicians, researchers, developers, and engineers who work in or are interested in fields related to IoT. This book serves as a reference for graduate and postgraduate courses in computer science, computer engineering, and information technology streams.