This document discusses Rogers' diffusion of innovations theory, which describes how new ideas and technologies spread through populations over time. The key aspects covered are: (1) the innovation-decision process that individuals go through in adopting an innovation; (2) how innovations are communicated through social networks via opinion leaders and communication channels; and (3) how the rate of adoption follows an S-shaped curve as innovations are adopted by different categories of individuals from innovators to laggards. The social system and its norms also influence how quickly innovations are diffused.