Abstract : This thesis aims to better explain the heterogeneity and the evolution of institutional pressures in a population of organizations. We propose that the study of the institutional influence and sensibility of organizations are major but under-exploited factors regarding this heterogeneity in literature. The adoption of a practice incarnating an institution reflects commitment to this institution, modifies it, enforces it and influences other organizations. Higher or lower sensibility of organizations towards this influence determines part of its propensity to adopt the practice. We try to demonstrate the importance of institutional influence and sensibility of organizations among French health organizations. The adhesion of organizations to the hygienist institution, reflected between 2000 and 2004 by the adoption of a « centralized collection of information regarding nosocomial infections », shows that this theory is valid, but also complementary and strongly significant regarding other well established sociological theories such as homophilia, network theory and organizational inertia. It allows solving the following ambiguity : public hospitals that have already adopted exert a higher influence on the adoption by other organizations, whereas private clinics have adopted more, but with a lower impact on other organizations. We show that this theory can lead to solve several ambiguities spotted in the literature.