This book provides a brief introduction to the history and evolution of the internet. Then, it introduces the Internet of Things (IoT), which is followed by a list of application domains and enabling technologies. The wireless sensor network (WSN) is presented as one of the most important elements in IoT networks, and the book describes the relationship between WSNs and the IoT. This book is concerned with developing energy-efficiency techniques for WSNs that enable the IoT. After having identified sources of energy wastage, the book reviews the literature that discusses the most relevant approaches to reducing the energy consumption of IoT and WSNs. The book also identifies a gap in the existing literature in terms of energy conservation measures that could be researched and, if successful, undertaken.