Decision taken during the Fuzzy Front End (FFE) have a high impact on the outcome of the innovation process. Therefore, product designers need methodologies and tools to manage innovation projects during these steps. A review of the literature was used to clarify the concepts of needs and requirements and how they relate to each other. The main contribution of this research is to define a methodology allowing the passage from need to requirement within an innovation process. A step-by-step methodology based on models is proposed starting with the description of users functioning modes, including the analysis of dependencies users face to achieve their own objectives and then allowing the elaboration of requirements lists. A case study is presented to illustrate this methodology.