In the late 1970s, a new research impetus occurred in the new product development literature with the publications of Eric Von Hippel's two seminal investigations (1976; 1977), where he advocated the involvement of users in the idea generation stage of the new product development process. Von Hippel"s conceptualisation of a customer active paradigm (1978) gave focus to a new generation of researchers and an emerging field of study into the involvement of users not only in the creation of ideas but to the whole new product development process. Over the last 25 years an impressive body of research has accumulated on the topic of user involvement and the purpose of this article is to synthesise and analyse that literature in order to assess the research progress in the area and also to assess our understanding of involving users in the development process. Based on the evidence reviewed, observations are drawn for future theoretical and empirical development in the field of user involvement