Geographical frontier phenomena may be considered at two levels. The larger consists of exchanges that cross borderlands without any direct impact upon them. The second consists of geographical problems that are of specific interest to the small border areas. The French-Belgian borderlands which have for two centuries constituted the region lying between the North Sea and Luxembourg can be divided into two series : — (1), the rural and forested areas, — (2), the urban border areas. The rural and forested border areas have in common a weak degree of polarisation. In fact, the polarised area generally, does not actually go beyond the border itself. How-ever some of them are crossed by heavy traffic of travellers and goods, the impact of which is very weak upon the small area. To that group belong the predominantly forested areas from Thierache to Lorraine, the rural areas of Flanders, Pevele and Hainaut. Their common problem is one of harmonising the policies of two States so as to preserve the landscape and safeguard its use for leisure activities. The urban areas consist of twin towns — especially in the Lys valley — of rail centers, of seaside resorts and of the Regio Insulensis, the metropolis of the French Region du Nord and of its Belgian counterpart. The continuity in the built-up area may be observed in many ways in the townscape. The journey-to-work, as well as leisure and consumption trips are much more intensive than in any of the rural border areas. In spite of the very real permeability of this frontier and the reality of the Common Market, the border as a boundary of State sovereignty is definitely slowing the development of the borderlands. Nevertheless we may hope that new kinds of trans-border cooperation will appear in such matters as industrial development or regional planning, especially in the Regio Insulensis. Inside the countries that are members of the E.E.C., the Regio could be an original example of a city region that extends through frontiers.