Robotics is a key technology in the modern world, a well-established part of manufacturing and warehouse automation, assembling cars or washing machines, or moving goods to and from storage racks for Internet mail order. Robots have taken their first steps into homes and hospitals, and have seen spectacular success in planetary exploration. Yet despite these successes, robots have failed to live up to the predictions of the 1950s and 60s, when it was widely thought--by scientists as well as the public--that we would have, by now, intelligent robots as butlers, companions, or co-workers. This...