The most striking feature of diffusion theory is that, for most members of a social system, the innovation-decision depends heavily on the innovation-decisions of the other members of the system. In fact, empirically we see the successful spread of an innovation follows an S-shaped curve (23). There is, after about 10-25% of system members adopt an innovation, relatively rapid adoption by the remaining members and then a period in which the holdouts finally adopt. I will review Rogers’s assessment of the factors affecting the adoption of an innovation with the goal of elucidating how the earlier adopters of an innovation profoundly affect the innovation-decisions of later adopters.