This book aims to spark curiosity about energy efficiency and energy management through a comprehensive presentation of the topic, encouraging the implementation of modern energy-saving measures without compromising residential comfort. It addresses the entire value chain, from decentralized energy conversion to energy consumption by end customers, while highlighting various societal action areas. Designed as an interdisciplinary technical book, it requires a technical understanding of the presented technologies. Additionally, it seeks to illustrate economic, socio-ethical, environmental policy, and ecological trends.