Why did it take cameras more than 50 years to start spreading from professionals to the general public? How did Sun Microsystems use the networks to spread the word about Java? How did the makers of Trivial Pursuit create huge demand for the game almost overnight? How did Nintendo create unprecedented buzz for Super Mario Brothers? Word-of-mouth has long been recognized as a powerful marketing tool and the revolutionary ability of the Internet to connect customers to each other now makes it absolutely critical. As customers grow ever more sceptical, they may not listen to adverts, but they do listen to their friends. This book teaches in a systematic way how these invisible networks work. Readers can learn how to: build contagious attributes into the product at design stage; identify "network hubs" that influence others in the network; seed non-active networks early on; and design "tell a friend" promotions that really work (they usually don't).