Part I. Foundations: Ten chapters lay a foundation in device physics, noise, and feedback systems including nano scales in a highly original fashion, emphasizing intuitive thinking. This foundation is important in designing and analyzing ultra-low-power systems in both electronics and biology; Part II. Low-Power Analog and Biomedical Circuits: Five chapters present building-block circuits that are useful for ultra-low-power biomedical electronics and analog electronic systems in general; Part III. Low-Power RF and Energy-Harvesting Circuits for Biomedical Systems: Three chapters provide an in-depth description of energy-efficient power and data radio-frequency (RF) links that are fundamental to biomedical systems; Part IV. Biomedical Electronic Systems: Two chapters provide an in-depth look at ultra-low-power implantable electronics and ultra-low-power noninvasive electronics for biomedical applications, respectively. Case studies for cochlear implants for the deaf, brain implants for the blind and paralyzed, wearable cardiac devices, and biomolecular sensing are provided; Part V. Principles for Ultra-Low-Power Analog and Digital Design: Two chapters discuss principles for ultra-low-power digital design and ultra-low-power analog and mixed-signal design, respectively. The chapters identify ten fundamental principles that are common in both biology and electronics, analog and digital design; Part VI. Bio-Inspired Systems: A chapter on neuromorphic electronics discusses electronics inspired by neurobiology followed by a chapter that discusses a novel form of electronics termed Cytomorphic Electronics, electronics inspired by cell biology. These chapters discuss applications of bio-inspired systems to engineering and medicine, deep connections between chemistry and electronics, and provide a unifying viewpoint of ultra-low-power design in biology and in electronics; Part VII. Energy Sources: A chapter on batteries and electrochemistry discusses how batteries work from a unique circuit viewpoint. The last chapter discusses energy harvesting in biomedical systems at portable scales (vibration and body heat) and at larger scales (low-power cars and solar cells). Principles of low-power design are shown to extend from small scales in electronics to larger scales and to non-electrical systems. This book reveals the deep connections between energy use and energy generation, vital for sustainable energy systems of the future.