Based on an analysis of oral and written archives, this article revisits the top down interpretation of French-style regionalization by showing the conditions in which this question appeared in the immediate post-war period. Far from being the exclusive product of the upper administration, regionalization was carried out on the basis of interactions and exchanges among a great variety of political and administrative actors (the federalist movement, planners, elected local officials, lobbies) active in the central political arena as well as in more peripheral ones (regional configurations). More generally, regionalization can not be separated from the debates of the inter-war and post-war periods about French and European political and soci...