This text presents coverage of all the layers of the design hierarchy, ranging from the technology, circuit, logic and architectural levels, up to the system layer. It gives insight into the mechanisms of power dissipation in digital circuits and presents state of the art approaches to power reduction. Finally, it introduces a global view of low power design methodologies and how these are being captured in the latest design automation environments. The book should serve as a broad introduction for anyone interested in low power design. It can also be used as a text book for an advanced graduate class, or a starting point for any aspiring researcher.