Until recently, the idea of holding a conversation with a computer seemed pure science fiction. If you asked a computer to "open the pod bay doors"—well, that was only in movies. But things are changing, and quickly. A growing number of people now talk to their mobile smart phones, asking them to send e-mail and text messages, search for directions, or find information on the Web.
Progress has come about thanks in part to steady progress in the technologies needed to help machines understand human speech, including machine learning and statistical data-mining techniques. The most prominent example of a mobile voice interface is, of course, Siri, the voice-activated personal assistant that comes built into the latest iPhone. But voice functionality is built into Android, the Windows Phone platform, and most other mobile systems, as well as many apps. While these interfaces still have considerable limitations, we are inching closer to machine interfaces we can actually talk to.