Book excerpt: This book explores the design of ultra-low-power radio-frequency integrated circuits (RFICs), with communication distances ranging from a few centimeters to a few meters. The authors describe leading-edge techniques to achieve ultra-low-power communication over short-range links. Many different applications are covered, ranging from body-area networks to transcutaneous implant communications and smart-appliance sensor networks. Various design techniques are explained to facilitate each of these applications.