This chapter introduces relational thinking about cities. The relational thinking I am interested in is not that which focuses upon one city and asks about its internal relations or how it relates to its hinterland. In this text, cities will always be referred to in the plural because the focus is on inter-city relations, on dependencies and interdependencies between cities. These can never be adequately understood by starting from just a single city, because inter-city relations form conﬁgurations of connections across many cities. In addition, the conﬁgurations I concentrate on are those that directly inform a material understanding of cities, how cities work together as economic entities. And although the book as a whole aspires to contribute to debates concerning the nature of contemporary globalization, issues that arise are by no means unique to these ‘global times’: ultimately, what I present is a geohistorical interpretation of world cities in networks. In this chapter I provide some necessary background – historical and literature reviews – for considering the different forms that inter-city relations might take.