The necessity to adapt the energy system due to limited energy resources and environmental damage, e.g. climate change, is today widely accepted. To understand, discuss, and manage the adaption a basic knowledge on the technologies used in the energy system is needed. The book tries to give a brief introduction in a way that is suitable for people without a higher scientific or technical education. It focuses on basic effects and general concepts, and tries to explain how things work without complex formulas; only basic physics and chemistry at a high school level is used. Crucial points are illustrated by examples. Additional information given includes sources of short movies in the internet that describe different technologies, often in action, and can be especially helpful for teaching. Further on, sources with a detailed scientific and technical treatment to go beyond a brief introduction are given. The book covers the essentials regarding energy, the different energy technologies, and finally how the different technologies are combined forming the energy system. The essentials introduce and explain the different energy forms, as there are mechanical, thermal, electrical, magnetical, chemical, and nuclear energy, the different types of processes of energy conversion, storage, and transport, and the exchange of energy as work and heat. Following the essentials is the description of the individual technologies for energy conversion, storage and transport. For each of them, the basics and the different technologies are discussed, starting from single step processes, as in materials, to multiple step processes, as in power plants. In the energy system, many of these technologies are connected to supply the desired energy to the user. Basic considerations on energy networks, a description of networks for thermal, electrical, chemical, and nuclear energy individually and their connections in the global energy system conclude the book.