A milieu is not immutable, it is not defined a priori, once and for all. On the contrary, it constitutes a dynamic complex which in the course of time has had to change and evolve through a continuous process of resource creation, innovation and adaptation to external constraints. The milieu thus obviously contains an historical dimension and complies with a life cycle (Perrin, 1993). This observation invites the researcher to transcend an issue centred on the milieu’s modes of operation and the study of its strategies and players and to address the question of the origin of qualitative changes in, and the emergence, development and decline of, the milieu. This study therefore sets out to explain the route or path of development followed by the milieu over the long term, as well as to understand the processes at the basis of its transformations. In this respect it seems essential to analyse the milieu’s different modes of response, particularly adaptation of its internal structures to global technological and economic changes. To do so, a long-term, comparative investigation is necessary which encompasses the nodal phases of the milieu’s development.