Book excerpt: A new, counterintuitive theory for how social networks influence the spread of behavior New social movements, technologies, and public-health initiatives often struggle to take off, yet many diseases disperse rapidly without issue. Can the lessons learned from the viral diffusion of diseases improve the spread of beneficial behaviors and innovations? How Behavior Spreads presents over a decade of original research examining how changes in societal behavior—in voting, health, technology, and finance—occur and the ways social networks can be used to influence how they propagate. Damon Centola's startling findings show that the same conditions that accelerate the viral expansion of an epidemic unexpectedly inhibit the spread of behaviors. How Behavior Spreads is a must-read for anyone interested in how the theory of social networks can transform our world.