Climate change has, more than anything else, imposed innovative challenges for present human energy systems. This course begins with an overview of global energy systems based on oil, carbon, nuclear and hydro power as well as supplementary systems. The overview includes resources/reserves of non-renewable energy sources, carbon capture and storage, climate and energy politics. Basic concepts, such as primary energy, conversion, emission factors, final use, energy carriers, energy, and power units are presented and problemised. Three areas are given particular emphasis: firstly, energy end use efficiency, its historical development and future prospects; secondly, renewable energy and the ongoing change at its technological frontier; thirdly, transports, their different systems, use of energy and impact on the environment as well as ongoing technological change. Both positive and normative aspects of the interplay between economic growth and energy are examined. Among the first aspects is the so called decoupling of energy and GDP, as well as CO2 and GDP. Relative and absolute decoupling is a central distinction of crucial importance for the sustainability of an energy system. Evidence and explanations for past decoupling are scrutinized, such as the third industrial revolution and the transition from commodity production to services. Normative aspects consider institutional and political factors which determine incentives for innovation.