With a long-term historical perspective, the processes of transformation and the continuities in the social, economic and territorial organization of Cerdaña, a Catalan Pyrenean plain, are traced. Divided in 1659 by the Treaty of the Pyrenees between France and Spain and submitted in 1833 to the new provincial division in Spain, there is a marked permanence of community sentiment, as an agricultural unit until the early twentieth century. The border controls, far from dividing the community, reinforced the reproduction of family and community interests, which were governed by medieval Catalan Civil Law, and by the set of agreements between communities that regulated the use of collective goods. The processes of tertiarization of the economy (second residences and winter sports) have transformed in a few decades the patterns of behavior and collective identity to a greater extent than did centuries of control and regulation of the absolute monarchies or the liberal state.