Going ‘back to basics’ translates into searching out city networks. This leads to many new questions, not least of which is ‘what sort of network?’. In this chapter I provide an answer to this and other questions such as ‘how are cities connected to each other?’ and ‘how can a city’s connectivity be measured?’. Asking such questions is itself an important step because past concepts used to describe how world cities relate to one another have been notoriously vague in such matters. As well as Friedmann’s familiar ‘world city hierarchy’, there is reference to, among others, ‘global network of cities’ (King 1990: 12), ‘transnational urban system’ (Sassen 1994: 47), ‘new global urban hierachy’ (Wu 1996: 121), ‘functional world city system’ (Lo and Yeung 1998: 10) and ‘global urban network’ (Short and Kim 1999: 38). In using these concepts, none of the authors speciﬁes their construct in a manner that allows answers to be given to the sort of questions just posed. The purpose of this chapter is to present a precise speciﬁcation of a world city network in order to begin the task of measuring world city network relations.