Today, we are witnessing a growing enthusiasm for inter-organizational cooperation, as it has become the best path for managing organizations. Several authors and practitioners consider confidence as essential for the development and sustainability of this cooperation. According to Gambetta (1988) [1], confidence promotes cooperative behavior and promotes relationships between cooperants. For Social and Solidarity Economy organizations, inter-organizational cooperation is an excellent way to demonstrate the proper use of the principles of confidence. This is a key factor in their success, which is reflected in the practice of their daily activities. Thus, drawing inspiration from the literature dealing with confidence, and according to the measurement criteria proposed by Mayer & al., (1995) [2], we are conducting a quantitative study with three Economic Interest Groups (EIG) and four unions, composed of 59 cooperatives operating in d'Argane, located in Souss-Massa region. The goal is to show how confidence is built within these organizations. To what extent it influences inter-organizational cooperation.