This chapter seeks to investigate whether the proximity of a border can be seen as an engine of regional development, or a disruptive element. The impacts of cross-border activity on demographic evolution but also on unemployment or economic activity at the French–Luxembourgish border will be identified. Quantitative data from the municipal level (French census for 2014) will be used, with a special focus on the French border municipality of Longwy (formerly one of the main steel-producing areas in France).