This document is the third edition of Everett Rogers' book Diffusion of Innovations. It provides an overview of diffusion research from the early 1900s to the 1980s, summarizing key findings and theories. The book also critiques past diffusion research and proposes directions for future research. With over 3,000 publications on diffusion, it is one of the most widely researched topics in behavioral science. This edition aims to both continue and advance the theoretical framework for understanding the diffusion of new ideas and technologies.