Recent advances in the field of computer vision are leading to novel and radical changes in the way we interact with computers. It will soon be possible to enable a computer linked to a video camera to detect the presence of users, track faces, arms and hands in real time, and analyze expressions and gestures. The implications for interface design are immense and are expected to have major repercussions for all areas where computers are used, from the work place to recreation. This book collects ideas and algorithms from the world's leading scientists, offering a glimpse of the radical changes around the corner that will alter the way we interact with computers in the near future.