This thesis takes an interdisciplinary approach to research how design rationale may improve practices for participatory design in urban planning. Knowledge on sustainable development, participatory planning in public sector, design rationale and innovation are brought together to form a cohesive understanding for the matter of citizen dialogue and participation.  To further gain knowledge on the subject a case study is done following the planning of a consultation at the urban planning office in Norrköping by participatory observations. Furthermore, semi-structured interviews are conducted with civil servants from Norrköping and Norrtälje, discussing the theme of citizen dialogue and municipal capacity and competence for its performance. The knowledge contributions addresses the specific case study at first hand, but are also applicable in some general sense. The study shows that design rationale can be of use and inspiration to address issues of culture and mental models in public sector, as these as believed to stand in the way of forming a more innovative and adaptive public sector that can design better practices for dialogue and participation. Design thinking and attitude can bring openness and human centred perspectives, among other things, to public organisations.  For the case study in question it is suggested that the urban planning office would benefit from implementing and trying out ways of working that are more in line with design thinking and attitude. It is also suggested that they might benefit from employing an experienced designer to be part of planning procedures, as expert designers can adapt methods and tools for participation to design case specific activities. To employ a more case specific and local approach to participatory practices is proposed to bring better results, both in terms of its democratic breakthrough as well as its impact on social sustainability.  Overall, this thesis offers contributions to design knowledge, knowledge that in turn can be important for the area of sustainable development at large.