This paper highlights three dimensions of competencies: individual, collective and social. In this perspective, we assume that workers are in a situation of both productive interdependences and social interactions within the firm. Each worker is identified in terms of his or her social group (gender, age, nationality). Inter- and intra-group interactions determine their competencies and thus their productivity. It follows that individuals' competencies depend not only on their skills but also on their social category and the socio-demographic composition of the workforce. The empirical results obtained, based on data drawn from the 1997 Organizational Change and Computerization survey, confirm this triple dimension of competencies: individual, collective and social.