PREFACE In the cavern of the Nome King Shaggy replaced the wireless telephone in his pocket and turning to Betsy said in as cheerful a voice as he could muster: "Well, little comrade, what shall we do next?" - L. Frank Baum, Tik-Tok of Oz, 1914 Writing about ubiquitous computing is like trying to draw a supersonic plane as it's flying overhead. At best you can try to get the general outline, and leave the details a blur. This book comes very early in a time of major technological shifts in the world. We're still coming to terms with the changes brought by the Internet and mobile telephony, which are merely the latest examples of an even larger shift brought by the computational manipulation of information. Saying anything about future changes with any degree of certainty is difficult and likely futile. In 2005, I first proposed this book as a series of descriptive case studies of