In previous chapters of this book, we emphasized the importance of interpersonal network influences on individuals in convincing them to adopt innovations. Here we summarize what is known about such diffusion networks and how they convey innovation evaluation information to an individual in order to decrease uncertainty about a new idea. We begin with a discussion of opinion leadership, the degree to which an individual is able informally to influence other individuals’ attitudes or overt behavior in a desired way with relative frequency. Opinion leaders are individuals who lead in influencing others’ opinions. The behavior of opinion leaders is important in determining the rate of adoption of an innovation in a system. In fact, the diffusion curve is S-shaped because once opinion leaders adopt and begin telling others about an innovation, the number of adopters per unit of time takes off in an exponential curve.