The thesis seeks to demonstrate that during the period between 1986 and 2006, some of the principal cities of the Spanish metropolitan system1, have undergone significant change in terms of their European competitiveness. It is suggested that in the case of Madrid and Barcelona in particular this change has been of such a magnitude to proportion them a much more important place within the European spatial configuration than that which they occupied in the mid-1980s. Empirical evidence is offered to support this conjecture. The thesis lies wholly within the framework of spatial planning at the European territorial scale.It charts the comparative ascent of the Spanish cities from the moment of Spain's entry into the European Union (EU) in 1986 against the background of the development of European spatial policy, increased economic integration across Europe, the increased importance of the 'territorial' dimension of EU cohesion policy and an eventual waning of the applicability of the terminology of 'core' and 'periphery' to describe European geographical location.Part One (Chapter 1) addresses the processes of urbanisation in general from a global perspective and then focuses on metropolitan growth in a number of different historical contexts from the start of the 19th Century. Parts Two (Chapters 2-5) and Three (Chapters 6-9) of the thesis carry out analyses at two contrasting but complementary spatial scales. Part Two examines the metropolitan growth processes in Spain, in the period since 1857, detecting the historical moments in which there were surges in the metropolitan populations of the seven cities of the metropolitan system. The dimensions of the spatial units of analysis corresponding to the seven Spanish metropolitan urban regions are described, based upon a methodology first developed by the Universitat Politècnica de Catalunya (UPC) in the context of a transnational spatial planning project of the INTERREG community initiative2. These seven spatial units form the basis for a socio-economic analysis of the structure of the metropolitan system, drawing upon data principally from the 2001 Census. If by 1930 one of the key characteristics of Spain's urban system was having not just one but two cities (Madrid and Barcelona) belonging to the group of 27 cities across the world with populations in excess of 1 million inhabitants3, this same differentiation between the country's two largest cities and the remainder of the urban system is equally valid today. Spain's urban system remains clearly bicephalous in being dominated by these same two cities in terms of demographic and economic strength.Part Three begins by examining the evolution of European spatial policy against the background of an ever-enlarging European Union and changes with regard to the notion of cohesion - from a concept understood in terms of economic and social factors, to one in which the territorial dimension has become increasingly important. The European urban system is then critically examined through a number of key and influential studies, with particular regard to the rankings and hierarchies of metropolitan urban regions deriving there from and the changes in the placing of the Spanish metropolitan urban regions therein.Taking inspiration from the seminal contribution of Manuel Castells4 in the context of the structural changes resulting from the informational and technological revolution, the thesis seeks to replicate the concept of a 'space of flows'. This is carried out through a 'network analysis' approach drawing upon air passenger flows between some 28 European metropolitan urban regions of the EU15+2 group of countries, enabling the analysis of the interaction between these 28 cities. This methodology enables arriving at a number of descriptive indicators which in turn, through the application of a multi-dimensional scaling mathematical technique, permits comparing the functional and physical distances of each of the metropolitan urban regions from the centre of the 'conceptual space of air passenger flows' and the centre of gravity. The resulting map of the functional positioning of the cities offers a spatial vision of metropolitan Europe quite different to that based upon Cartesian coordinates. Such an approach enables demonstrating that cities such as Barcelona, Madrid, Helsinki, Lisbon and Athens, traditionally considered as physically peripheral to the European core area, appear to be more favourably positioned in functional terms. Furthermore in the case of Spain the results indicate that Barcelona lies closer to the centre of the conceptual 'space of air passenger flows' than Madrid.In light of this empirical evidence, together with the signs of increased economic integration across some parts of Spain, the prospects of Spain forming part of a wider European territorial concentration of flows and activities, and the recognition of the territorial capital of Madrid and Barcelona within recent EU spatial policy declarations, the thesis concludes in Part Four that these two metropolitan regions have undergone a clear consolidation and (re)positioning within the European metropolitan hierarchy.