**1. Introduction**

Energy has emerged as the unspoken life force that sustains our world in the modern era. From powering our homes, propelling our vehicles, and fueling the engines of industry, energy underpins nearly every aspect of our lives. Energy influences our economies, geopolitics, and environment, and the importance of energy cannot be overstated. The global growth of energy demand is accompanied by rising prosperity and better life quality. Energy consumption, storage, conversion, and efficiency are interconnected components of the world energy system, each playing an important role in shaping our energy landscape. This chapter presents an introductory review of energy consumption, storage, conversion, and efficiency, inviting us on a journey into the intricate interplay of energy within our society.
