This thesis explores demonstration projects as a potential strategy for supporting processes towards sustainable development in the building sector through making mainstream building more sustainable. The research question has been approached in four empirical studies carried out in Sweden and the Netherlands, which study demonstration projects for sustainable housing from different perspectives. These are: 1) two case studies, 2) qualitative interviews with key actors, 3) a study of the image conveyed by the Swedish trade press, and 4) a study of the image conveyed by <i>The Swedish Architectural Review</i>. The findings are discussed using a framework presenting the notions of sustainable development and sustainable building, conditions for learning and development in the building sector as well as the findings from earlier research in the field. The thesis indicates that demonstration projects have an important role in the processes towards sustainable development in the building sector. The demonstration project provides real-world data, makes sustainable building a tangible and visible concept and is a means of learning through doing for the actors involved. The demonstration project becomes a reference to what sustainable building is and how this can be accomplished. The demonstration project has the potential of becoming a strategy for systematic successive learning and development on the path to reaching long-term abstract objectives for sustainable development through realistic advancements and in accordance with conditions for learning and development in the building sector. However, in order to become an effective strategy, deficiencies in contemporary demonstration projects have to be solved. This concerns the lack of incentives and interest for learning; deficiencies in the production of reliable and useful information; and the lack of institutions for information dissemination. The fact that demonstration projects are handled as special projects also impedes their influence on mainstream building. Moreover, ideals in contemporary demonstration projects often fail to address ideals and interests among actors in the building sector. The thesis provide a basis for the enhanced understanding and use of demonstrations projects, both from a theoretical and a practical view, and discusses the production and dissemination of reliable and useful information as well as factors that will affect the influence of demonstration project on mainstream building