This book provides a comprehensive treatment of CMOS circuits for passive wireless microsystems. Major topics include: an overview of passive wireless microsystems, design challenges of passive wireless microsystems, fundamental issues of ultra-low power wireless communications, radio-frequency power harvesting, ultra-low power modulators and demodulators, ultra-low power temperature-compensated current and voltage references, clock generation and remote calibration, and advanced design techniques for ultra low-power analog signal processing.