The diffusion of innovation theory provided the basis for a model of agricultural development that the extension service continues to use today. This study aims to examine the history, influence, and impacts of innovation diffusion theory on the extension service. It reviews some of the major developments in the literature related to the theory, examines its criticisms, and discusses the implications for extension. As such, innovators are younger, more cosmopolitan, have higher incomes than later adopters, and have the largest operations of all adopter categories. There are two critiques on diffusion of innovation theory in which are the method and inequity recurring from diffusion.