The Berkshire Encyclopedia of Human-Computer Interaction takes computing into new realms, introducing us to topics that are intriguing both in their technical complexity and because they present us - human beings - with a set of challenging questions about our relationship with ""thinking"" machines. There are opportunities and risks in any new technology, and HCI has intrigued writers for many decades because it leads us to a central philosophical, religious, and even historical question: What does it mean to be human?