How is Globalisation changing the form and spatial structure of cities today? Deceptively simple, this question presents us with a number of methodological challenges and unanswered theoretical problems. What is globalization? Can we define a series of distinctive new phenomena constituting a coherent and logical outline? Do these phenomena influence the structure of cities today? If so, how? Our hypothesis is that processes related to globalisation have resulted in convergent transformation in urban spatial structure in some areas of global cities. However, convergent transformation emerges from very particular spatial, historic and social contexts. Old and new processes are in constant interplay and spatial outcomes are very different at first sight. The dichotomy between 'globalizing' and 'non-globalizing' spaces may contribute for social and spatial division and polarisation in cities. It also represents a new challenge for planners, who have to deal with often contradictory processes stemming from the global and local arenas. The primary hypothesis is supported by empirical evidence on the location patterns of command activities in the Randstad-Holland and Sao Paulo Metropolitan Region. Impacts on the distribution of economic activity, the constitution of business centralities and changes in spatial structure are evaluated in the two cases. We conclude that despite time-space compression caused by developments in transportation technologies and ICT, there is an enduring tendency towards agglomeration of advanced services. We argue that this is a result of the role played by urban technical networks and urban milieux in the organisation of economic activity. We simultaneously emphasize the importance of accessibility, visibility and face-to-face contacts, as necessary elements for the development of synergies between different agents: the urban 'buzz', essential for the appearance of innovation and creativity. The organisation of functional networks in urban territories where global flows are intense ('global cities') obeys a new logic derived from the acceleration of flows and increasing complexity of functional and technical networks in Post-Fordism. These new logic has produced new polycentric urban landscapes, with 'corporate centralities' structured around hubs of connectivity and transferability, where the transfer between several scales of operation (from local to global) is facilitated.