This research thesis is an empirical investigation of how changing patterns of employment geography are affecting the transportation sustainability of the London region. Contemporary world cities are characterised by high levels of economic specialisation between intra-urban centres, an expanding regional scope, and market-led processes of development. These issues have been given relatively little attention in sustainable travel research, yet are increasingly defining urban structures, and need to be much better understood if improvements to urban transport sustainability are to be achieved. London has been argued to be the core of a polycentric urban region, and currently there is mixed evidence on the various sustainability and efficiency merits of more decentralised urban forms. The focus of this research is to develop analytical tools to investigate the links between urban economic geography and transportation sustainability; and apply these tools to the case study of the London region. An innovative methodology for the detailed spatial analysis of urban form, employment geography and transport sustainability is developed for this research, with a series of new application of GIS and spatial data to urban studies. Firstly an intra-metropolitan scale of spatial analysis is pursued, allowing both an extensive regional scope and a sufficiently intensive local level of detail to analyse the decentralisation processes described above. Secondly a series of detailed spatial datasets are introduced to analyse employment geography and dynamics, including business survey data and fine-scale real-estate data. For the measurement of accessibility, detailed network analysis and congestion data is used. Finally for the assessment of transportation sustainability, an indicator of CO2 emissions at intra-urban scales is developed, and is calculated for the 6.5 million journey-to-work trips in the study region. The results highlight extreme intra-urban variation in accessibility, employment geography and travel carbon emissions with clear relevance to urban form and sustainable travel debates in the London region.