This article presents a method used in the context of a participative approach under the shape of a research-action led for two years in a city of 12 000 inhabitants in French-speaking Switzerland. Elements of the theoretical framework, the process and the methodology of organized intervention are clarified. We also present the implementation plan as well as the interactive activities developed to collect data in a participative diagnosis and we communicate some recommendations delivered to the politicians who sponsored this research. We conclude by a reflection on the conditions of a real citizen participation and on the way of setting up devices allowing it.