The need for “green” systems has grown substantially over the last years. For a long time power has been a major design point mainly in the domain of handheld and battery operated devices. Driven by growing power density, rising energy cost, new legislation, environmental issues and the public awareness for it, power and energy efficiency is now more and more becoming a key differentiator for market success in almost all areas comprising microelectronic systems. Nowadays, power has to be taken into account in all development and fabrication steps, leading to new challenges in all areas from architectural planning to the final system. Starting from a background overview that shows the growing need for power reduction, this presentation will give an overview of state-of-the-art techniques to reduce power, giving a holistic view from chip level to system and application levels. Practical industrial examples show how power savings can be achieved in modern SoC, processors and computer systems.