This paper describes an approach for the participatory design. After describing the trends in the domain, a formalization of the design process is expressed based on « phase », « moment » and « primitive ». The phases articulate the design moments as nodes and transitions in a dynamic graph. The moments are built on reusable primitives defined as instanciable objects. Then, the paper details with this formal model a platform and tools for managing the design process on different points of view : from the user and engineers to the project manager. CATEGORIES AND SUBJECT DESCRIPTORS: H.5.2 [Information Interface and Presentation (e.g. HCI)]: User Interface---User-centered design. GENERAL TERMS: Design, Documentation, Experimentation, Human Factors, Standardization