Abstract : The emergence of new forms of industrial organization has been well observed so far. Many terms appeared to designate different evolutions of the traditional boundaries of firms: inter-enterprise networking, extended enterprise, agile virtual enterprise, and so on. Amongst all these new industrial architectures, this study focuses on networks of SMEs where firms are grouping together to achieve common goals, but strongly preserving their juridical independence. These new organisations need tools helping them to find out the most efficient organisational structure to be more competitive.This study provides a methodology to characterize objectively co-operation links and to identify potential ties for enterprise networks. It is based on a theoretical approach combining complementarity of activities and similarity of competences within firms. These two parameters are used to identify the preferential coordination mode between two enterprises within the network. An organisational map is plotted describing potential relationships within a group of firms. The evolution of the network is represented by a scenario tree according to an initial position and to possible changes of competencies and activities. It offers an efficient decision-making aid to the manager. Two case studies are presented to confront the proposed methodology to the reality.