Abstract In this thesis a new phenomenon called lay participatory design (PD) is described and defined. The work is based on a long-term historical and ethnographic field study in a non-profit community of dog breeders. The case community is committed to the understanding and support of indigenous dogs and their hunting skills through the improvement of breeding knowledge using information technology. This is conceptualized as a user-field-design perspective within a natural cultural historical IT context. The new design mode based on this perspective can be seen as infrastructuring, which integrates the activity, community, and IT. Once in actual use, new knowledge and IT is put into practice in the field, which is the actual focus of the change. As it is practice field-driven, lay PD differs conceptually and theoretically both from conventional and professional IT expertise and IS design models, and from representative-, design- or project-driven approaches to PD and to design ethnography. Because of the traditional division of labour in IS these approaches often take only the professionalized (IT) design as the starting point and ignore the epistemological interests of ordinary people, non-IT-professional users active in their own, everyday domains and in their own participative and collaborative practices in the field of practice. The use-field-design perspective, which is conceptualized in lay PD, is complementing these approaches because it takes seriously ordinary people/users as local designers who are competent with topics, everyday domains, activity and IT located in the related field of practice. The case shows that IT and the core activity of a community can be developed together, and that this co-development is sensible. The results of this study suggest that lay PD concepts can describe essential features of the design process for everyday communities of practice. As a bottom-up form of systems design using everyday knowledge, lay PD can be adopted in other domains and study areas. Thus, lay PD is one new member in the emerging family of Participatory Design, Social Shaping of Technologies, and End User Development-driven systems.