What is the importance of the study of frontiers and boundaries in political geography ? It has changed with the evolution of the domain, was preeminent between the two World Wars when the prime concern was with the regional differenciation of the earth surface. The contemporary renewal of political geography results 1) from the analysis of the communication Systems through which power controls space, and 2) from the integration of perceptual and representation facts. With such a view, it is easy to explain the variety of boundary types as noted by traditional geography and to place them along an evolutionary scheme. It is equally possible to understand the multiple effects that the contemporary growth of all forms of mobility exerts on the boundaries.