The ENS is a "grande école" and, as such, is not part of the mainstream university system, although it maintains extensive connections with it. The vast majority of the academic staff hosted at ENS belong to external academic institutions such as the CNRS, the EHESS and the University of Paris. This mechanism for constant scientific turnover allows ENS to benefit from a continuous stream of researchers in all fields. ENS full professorships are rare and competitive. Generalistic in its recruitment and organisation, the ENS is the only "grande école" in France to have departments of research in all the natural, social, and human sciences. Its status as one of the foremost centres of French research has led to its model being replicated elsewhere, in France (at the ENSes of Lyon, Paris-Saclay, and Rennes), in Italy (at the Scuola Normale Superiore in Pisa), in Romania, in China and in former French colonies such as Morocco, Mali, Mauritania, and Cameroon.