This lecture provides an overview of the energy system, covering different forms of energy, energy services, and the transformation process. It discusses the importance of understanding energy vectors, usable energy forms, and the role of refineries and power plants. The lecture also delves into the concept of energy conversion, distribution, and consumption, highlighting the elements involved in the energy system. Additionally, it explores global energy issues, renewable and non-renewable energy resources, and the historical evolution of the energy system from pre-industrial to modern times.