The great surprise of this book was how much it taught me about topics I never expected to find here: how new products spread (diffusion of innovation), the organization of firms, the differences between the spread of disease and the spread of computer viruses, and, of course, the six degrees of separation that supposedly exists among any two random people on the globe (basically false in detail but true in spirit, with the interesting issue being not why any two people can be linked through a small chain (some chains are as long as 25 intermediaries), but rather how anyone ever discovers the path). A fascinating book that introduces a new mathematical tool and its many fascinating variants that promises to have large impact on a surprisingly varied set of phenomena from many diverse fields. This is of special importance to social sciences and business. And on top of all this, the book is readable and engaging, with a lengthy, annotated bibliography. What more could one want?