A simple observation of two trends can prove beneficial if envisaged together to unlock new social and urban potentials. On one hand we are growing older faster, most of the time in places that are unadapted, isolated. We are also healthier and active longer. On the other hand smaller cities in Europe have undergone stagnation and decline. The process of global shrinkage particularly affects cities that are no longer able to “hook up” to the networks of modern global capitalism. Grey Matter contradicts the common place that activity and productivity belong solely to the youth and criticizes the segregation of seniors. It claims that a productive city can also be inclusive.There is an opportunity to revitalize existing urban structures by placing seniors at the heart of our urban life harnessing the total ecology of Health in cities to create new durable social and economical bonds questioning the place and cost of Health, integration, participation and new virtuous dependencies.