Since the early 1960s the government of the Kingdom of Saudi Arabia (KSA) has had several urban development strategies that have been designed to spearhead development through the deployment of internationally recognised architects and urban planners. The adoption of this strategy has opened debate on the paradigm shift away from restrictive planning regulations at both national and regional levels. The process has enabled foreign policies and ideas based on internationalisation to drive the new urban centre developments in Saudi cities including Riyadh and Dammam. In 2008, this key shift saw the traditional restrictive urban development strategies, which prescribed - among other things - the number of storeys a building could have, being replaced by a strategy permitting an unlimited number of storeys. This dissertation examines the role played by international firms of architects and developers in shaping how architecture is practised in the Kingdom. The process has led to the adoption of modern architectural styles and has advanced a modernised planning approach, whereby traditional architectural structures and the use of local materials have gradually been replaced by modern styles, high-tech buildings and the use of new foreign materials, causing the loss of historic buildings throughout the country. This is seen by many to constitute an injury to national culture and could lead to cultural conflicts that may be exacerbated by the possible importation of planning principles and regulations. A chronological review of internationalisation and how international architectural practices have been mobilised to work in the KSA reveals the impact of this process on the Kingdom's urban development. While this may be desired by the authorities, it has been argued that the process does not seem to provide any clear strategy for the implementation of the desired sustainable urban centre development in the KSA. Hence, in the absence of clear directives, international architectural firms operate their own set of sustainability criteria to deliver the desired urban centres in the Kingdom. There has been little or no research into the mobilisation of international firms and foreign policies, nor into the impact of internationalisation on the development of planning codes, the modernisation of urban centres and the sustainability approach espoused by the KSA's planning development strategy. This study investigates the impact of the participation of international firms in Saudi Arabia's urban development. Government planning regulations and master plans are reviewed and a case study is conducted to identify the factors behind the engagement of international firms in the delivery of two capital projects: the King Abdullah Financial District in Riyadh and the Central Business District in Dammam. The study also explores the concept of sustainability and the engagement of foreign firms from the perspectives of various stakeholders through face-to-face interviews and a structured questionnaire. It establishes how the role of internationalisation as a driver of policy mobility has impacted on the new sustainable urban centres and in addition, how internationalisation has been operationalised through the notion of sustainability. Although planning codes and regulations may have been developed with good intent by the international firms concerned, their implementation has not yielded the desired result of delivering sustainable urban centres in the KSA. Thus, there is a conflict between a rapid urban development which seeks to integrate historical and traditional contexts on one hand, and the continual import and impact of globalised morphologies on the other. This leads to clear demarcations in urban evolution, making this conflict one of the key characteristics of emerging urban centres in the KSA.