Paris and Madrid, two Western-European capital regions experiment intense population loss whereas their metropolitan areas grow both demographically and economically. Both central cities are aging at a faster pace than their surroundings. This research project will undertake an in-depth examination of the socio-demographic shifts in Paris and Madrid over the last decade to determine the intensity and geography of change in the two metropolitan areas, the emergent challenges resulting from population shrinkage, and the (in)effectiveness of planning responses.