The first of a planned trilogy, this book examines the proposition that "Information" is as much a part of the physical universe as energy and matter. The acceptance of such a proposition has profound implications for the physical sciences; it also lays the foundations for a general theory of information. This book is directed firstly at researchers in information theory and scientists in other disciplines. However, its relatively non-mathematical nature and accessible writing style place it at the "scientific" end of the spectrum of popular science books. A general theory of information will emerge in the second volume; the third will examine the mechanism and evolution of human and machine intelligence.