Following a methodological introduction of the international function of political border, the author examines the new Italo-Yugoslavian frontier traced out by the Paris treaty of 1947 and the London Agreement Memorendum of 1954. Originally an « iron curtain » type closed to international exchanges, the border slowly began to open following the Udine Agreements of 1955. Along a border line of 216 kms, frontier posts were progressively established, these were subdivided into first class international posts (transit with passport permitted) and second class local posts (transit with frontier papers of the population residing within 10 kms on both side of the border and in the two zones of the former Free Territory of Trieste) ; the latter are in turn subdivided into permanent and seasonal posts. The author compares the distribution of the frontier posts with the physical characteristics of the border and the social and economic conditions of the land strips facing the frontier ; he then analyses the gradual development of the movement of persons and goods between 1955 to 1972. In 1972, 90 million crossings were recorded in the two directions. Even though such a movement has a particular economic significance for the inhabitants of the frontier, its role in international relations must not be overlooked. This tendency is explained by the complementary economies of the two countries, by the development of the exchange of goods between the Western and the Eastern European countries, by the ethnic and cultural affinities of the frontier populations, and by the exigencies of recomposition of natural geographic units broken by the political border. Thus the border tends to become a line of attraction for the populations, as well as for the economic activities and European cultural formation, and it tends to realize a coordinated development of the Eastern Alpine Region, composed of Friuli-Venezia Giulia, Slovenia, Carinthia and Styria.