Suppliers' involvement in product design activities is considered as a competitive advantage by numerous companies. Thus, they wish to develop some of their relationships with suppliers towards more collaborative practices in design. This research-work contributes to suppliers' involvement in collaborative design. It is performed within a collaborative project carried out in partnership with the corporate purchasing and technical managers of six customer companies - BioMérieux, Bosch Rexroth Fluidtech, Salomon / Mavic, Schneider-Electric, SNR and Somfy. It aims at helping these companies located in Rhône-Alpes to manage such relationships with their key suppliers. Comanaged by an institutional partner, Thésame, this research project has a strong territorial challenge. A new evaluation paradigm is proposed to assess the performance of the relationship instead of the performance of the sole supplier. This research-work suggests a set of models and associated tools in order to build and manage successful partnerships in collaborative design with suppliers. A "constructivist" epistemological position coupled with a "research-action" approach were implemented. This leads us to improve the academic understanding related to extended design practices as well to propose operational tools to practitioners, namely: A model to evaluate the customer's ability to design with its supplier, A model to evaluate the supplier's ability to design with its customer, A model to evaluate the performance of the relationship in a collaborative New Product Development (NPD) project.
