The three articles in this special section address the use of computing services and technologies to augment human activities. Technology has long been used to augment our physical and cognitive abilities. Heavy machinery enables us to lift objects well beyond our strength, reading glasses correct and enhance our vision, and cameras capture memories for future recall. Wearable computing pioneered the integration of technology into our clothing and even our bodies, but ambient computing systems are also increasingly capable of supporting cognitive operations: a projected user interface, for example, can improve our sense of direction or ability to assemble a complex machine. Next-generation systems promise to augment our senses, voices, motor activities, and even our minds in unprecedented ways.