The focus in planning theory has up to date mainly been on how to plan, with normative notions at the core of a theoretical approach. Not much has been written about how professional city planners work when in the process of creating a city plan. Discussions of the theory/practice relation – such as the treatment of reflective practice and the discussions of the centrality of tacit knowledge in professional and everyday practical competence – has had a profound influence on the dominating conception of professional competence in many fields. What still needs to be analyzed and systematically described is what the planning practice actually is, as a practically occasioned phenomenon, something that has not yet been done in this field but in many others. The aim of the project is to investigate the performance of the planning process, with regards to the ways in which participants are made accountable for the ways of seeing and reasoning in the situations of planning. That is, this project aims at investigating how professional planners see and create a city in terms of a professionally competent vision with special regards to sustainable solutions. The study has the potential to contribute to the theoretical notions of reflective practice and tacit knowledge as well as to the concept and methods of sustainable solutions. Sustainability as a concept for city planning has been under scrutiny during the last decades and the studies have been directed upon what is ascribed to the concept, but also here this discussion has been on a theoretical level. This study aims at analyzing how professional planners perform as they are planning cities and therefore also at how sustainable solutions are put into practice and how the concept is discussed and included into the planning process as it unfolds before the practitioners’ eyes. The project therefore has the opportunity to contribute both to the theoretical level of how planners tacitly conduct planning and regard sustainability, how the concept of sustainability is practically applied and how the routine-like ordinary knowing-in-action is transformed into a professional planning process; the study will be relevant to work processes generally and to planning processes specifically. Studying practitioners at work makes it possible to get to the tacit knowledge that practitioners have, but is problematic to describe without looking at the practice itself. This study studies the practice of planning itself and can therefore help to reveal the tacit knowledge of practitioners. Methodologically, the study is placed within the tradition of ethnometodology, in this tradition the data can be collected during the actual process of work, i.e. during the work itself. The collection of data as the actions unfolds ’in situ’ is often done with the help of video recordings. This makes it possible to analyze the material with the actions and semiotic resources that the participants make use of at the core of the investigation. These recordings of the actions performed by the experts as they are in the process of planning puts the researcher in a passive role during the collection of Abstract Måns Norlin, Young Researchers Workshop, IAPS 2010 data. But the material can also be complimented with field notes and/or other metods included in the above examples if the material is question begging. When studying work processes the professional vision of the participants can be studied. Since the practical elements in the to be collected data of the planners work is to elaborate with different kinds of material in close collaboration with others, ’seeing’ professionally becomes a highly complicated communicative social practice. This dense material of a highly complex task that the planners perform is thereby studied in the tradition of ethnometodology and communication analysis.