Diffusion is a process by which information, viruses, ideas and new behavior spread over the network. For example, adoption of a new technology begins on a small scale with a few “early adopters”, then more and more people adopt it as they observe friends and neighbors using it. Eventually the adoption of the technology may spread through the social network as an epidemic “infecting” most of the network. As it spreads over the network it creates a cascade. Cascades have been studied for many years by sociologists concerned with the diffusion of innovation; more recently, researchers have investigated cascades for selecting trendsetters for viral marketing, finding inoculation targets in epidemiology, and explaining trends in blogspace.