This book, Ultra Low Power Bioelectronics, is about ultra-low-power electronics, bioelectronics, and the synergy between these two fields. On the one hand it discusses how to architect robust ultra-low-power electronics with applications in implantable, noninvasive, wireless, sensing, and stimulating biomedical systems. On the other hand, it discusses how bio-inspired architectures from neurobiology and cell biology can revolutionize low-power, mixed-signal, and radio-frequency (RF) electronics design. The first ten chapters span feedback systems, transistor device physics, noise, and circuit-analysis techniques to provide a foundation upon which the book builds. Chapters that describe ultra-low-power building-block circuits that are useful in biomedical electronics expand on this foundational material, followed by chapters that describe the utilization of these circuits in implantable (invasive) and noninvasive medical systems. Some of these systems include cochlear implants for the deaf, brain implants for the blind and paralyzed, cardiac devices for noninvasive medical monitoring, and biomolecular sensing systems. Chapters that discuss fundamental principles for ultra-low-power digital, analog, and mixed-signal design unify and integrate common themes woven throughout the book. These principles for ultra-low-power design naturally progress to a discussion of systems that exemplify these principles most strongly, namely biological systems.