Global urbanisation processes do not only account for quantitative growth, but also bring about qualitative transformations of our urban environments. They lead to the formation of new typologies of settlement forms. Besides the monocentric metropolises and mega-cities, we observe an increasing number of large-scale urban forms that grow together out of former single cities merging into one interconnected city-region. In many respects, Frankfurt Rhine-Main demonstrates the elements of a polycentric city-region, characterised by a network of large, medium-sized and minor centres that build up a system of decentralised centralisation. Challenges for sustainable development include the creation of integrated mobility systems, a nexus of settlement form and public transport, compact multi functional nodes, connectivity of regional open spaces and the conception of a common vision for the future.